From 86e320e1a5c5012db97422d5608fa2e80b438ad1 Mon Sep 17 00:00:00 2001
From: Aleksandr Penskoi <alexandr.penskoi@health-samurai.io>
Date: Fri, 24 Jul 2026 16:05:03 +0400
Subject: [PATCH 1/9] feat(typeschema): precompute derived slice facts on
 profile snapshots
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

FieldSlice gains effectiveRequired, constrainedChoice, autoStub and
resourceType, populated once at snapshot build. The TS and Python writers
consume them instead of re-deriving the same semantics per language, which
removes duplicated collectors and fixes two divergences that duplication had
already produced:
- Python auto-stubbed required slices that need user data beyond the
  discriminator match (e.g. US Core race/ethnicity text slices) — extension
  profiles now keep 'extension' as an optional create() param populated via
  sub-extension setters, mirroring the TS Raw type;
- validateSliceFields no longer requires choice-declaration base names
  (phantom 'value' key that never exists in FHIR JSON) inside slices.
---
 .../python/profile-factory.ts                 |  15 ++-
 .../writer-generator/python/profile-slices.ts |  42 +------
 .../python/profile-validation.ts              |  19 +--
 .../typescript/profile-slices.ts              |  66 ++--------
 .../typescript/profile-validation.ts          |  17 +--
 src/typeschema/types.ts                       |  11 ++
 src/typeschema/utils.ts                       | 114 ++++++++++++++----
 7 files changed, 138 insertions(+), 146 deletions(-)

diff --git a/src/api/writer-generator/python/profile-factory.ts b/src/api/writer-generator/python/profile-factory.ts
index 95fd182c..6cbd9609 100644
--- a/src/api/writer-generator/python/profile-factory.ts
+++ b/src/api/writer-generator/python/profile-factory.ts
@@ -175,10 +175,17 @@ export const collectProfileFactoryInfo = (
 
         if (isNotChoiceDeclarationField(field)) {
             const sliceNames = collectRequiredSliceNames(field, flatProfile.slicing?.[name]);
-            if (sliceNames) {
+            // Extension profiles populate `extension` via sub-extension slice
+            // setters — keep it optional in create() even when no slice is
+            // auto-stubbable (mirrors the optional `extension` in the TS Raw type).
+            const slicedExtensionProfileField =
+                name === "extension" &&
+                flatProfile.base.name === "Extension" &&
+                flatProfile.slicing?.extension?.slices !== undefined;
+            if (sliceNames || slicedExtensionProfileField) {
                 if (field.type) {
                     const pyType = fieldPyType(field, resolveRef, tsIndex);
-                    sliceAutoFields.push({ name, pyType, typeId: field.type, sliceNames });
+                    sliceAutoFields.push({ name, pyType, typeId: field.type, sliceNames: sliceNames ?? [] });
                     autoAccessors.push({ name, pyType, typeId: field.type, refComment: pyReferenceComment(field) });
                 }
                 continue;
@@ -269,7 +276,9 @@ export const generateCreateResource = (
         for (const f of factoryInfo.sliceAutoFields) {
             const fieldName = pyFieldName(f.name, fmt);
             const matchRefs = f.sliceNames.map((s) => `cls.${pySliceStaticName(s)}`);
-            if (matchRefs.length === 1) {
+            if (matchRefs.length === 0) {
+                w.line(`${fieldName}_with_defaults = list(${fieldName} or [])`);
+            } else if (matchRefs.length === 1) {
                 w.line(`${fieldName}_with_defaults = ensure_slice_defaults(list(${fieldName} or []), ${matchRefs[0]})`);
             } else {
                 w.line(`${fieldName}_with_defaults = ensure_slice_defaults(`);
diff --git a/src/api/writer-generator/python/profile-slices.ts b/src/api/writer-generator/python/profile-slices.ts
index 25fa7c3f..cf348984 100644
--- a/src/api/writer-generator/python/profile-slices.ts
+++ b/src/api/writer-generator/python/profile-slices.ts
@@ -1,7 +1,6 @@
 import {
     type ConstrainedChoiceInfo,
     type FieldSlicing,
-    isChoiceDeclarationField,
     isNotChoiceDeclarationField,
     isPrimitiveIdentifier,
     isTypeDiscriminated,
@@ -40,10 +39,8 @@ export const collectRequiredSliceNames = (
     fieldSlicing: FieldSlicing | undefined,
 ): string[] | undefined => {
     if (!field.array || !fieldSlicing?.slices) return undefined;
-    // Type-discriminated slices ("type" discriminator) require explicit typed setters — no stubs.
-    if (isTypeDiscriminated(fieldSlicing)) return undefined;
     const names = Object.entries(fieldSlicing.slices)
-        .filter(([_, s]) => s.min !== undefined && s.min >= 1 && s.match && Object.keys(s.match).length > 0)
+        .filter(([_, s]) => s.autoStub)
         .map(([name]) => name);
     return names.length > 0 ? names : undefined;
 };
@@ -93,52 +90,23 @@ export const normalizeMatchForPython = (
     return result;
 };
 
-const extractTypeDiscriminatorResource = (
-    isTypeDiscriminated: boolean,
-    rawMatch: Record<string, unknown> | undefined,
-): string | undefined => {
-    if (!isTypeDiscriminated || !rawMatch) return undefined;
-    for (const val of Object.values(rawMatch)) {
-        if (val !== null && typeof val === "object" && !Array.isArray(val)) {
-            const rt = (val as Record<string, unknown>).resourceType;
-            if (typeof rt === "string") return rt;
-        }
-    }
-    return undefined;
-};
-
 export const collectSliceDefs = (tsIndex: TypeSchemaIndex, flatProfile: SnapshotProfileTypeSchema): SliceDef[] => {
-    const pkgName = flatProfile.identifier.package;
     return Object.entries(flatProfile.slicing ?? {}).flatMap(([fieldName, fieldSlicing]) => {
         const field = flatProfile.fields[fieldName];
         if (!isNotChoiceDeclarationField(field) || !fieldSlicing.slices || !field.type) return [];
-        const choiceBaseNames = new Set<string>();
         const baseSchema = tsIndex.resolveType(field.type);
-        if (baseSchema && "fields" in baseSchema && baseSchema.fields) {
-            for (const [n, f] of Object.entries(baseSchema.fields)) {
-                if (isChoiceDeclarationField(f)) choiceBaseNames.add(n);
-            }
-        }
+        const typeDiscriminated = isTypeDiscriminated(fieldSlicing);
         return Object.entries(fieldSlicing.slices)
             .filter(([_, slice]) => Object.keys(slice.match ?? {}).length > 0)
             .map(([sliceName, slice]) => {
-                const matchFields = Object.keys(slice.match ?? {});
-                const required = (slice.required ?? []).filter(
-                    (name) => !matchFields.includes(name) && !choiceBaseNames.has(name),
-                );
-                const cc = slice.elements ? tsIndex.constrainedChoice(pkgName, field.type, slice.elements) : undefined;
+                const cc = slice.constrainedChoice;
                 // Skip flattening for primitive types — can't wrap/unwrap under a variant key.
                 const constrainedChoice = cc && !isPrimitiveIdentifier(cc.variantType) ? cc : undefined;
-                const typeDiscriminated = isTypeDiscriminated(fieldSlicing);
-                const typeDiscriminatorResource = extractTypeDiscriminatorResource(
-                    typeDiscriminated,
-                    slice.match as Record<string, unknown> | undefined,
-                );
                 return {
                     fieldName,
                     sliceName,
                     match: normalizeMatchForPython(tsIndex, slice.match ?? {}, baseSchema),
-                    required,
+                    required: slice.effectiveRequired ?? [],
                     array: Boolean(field.array),
                     max: slice.max ?? 0,
                     constrainedChoice,
@@ -146,7 +114,7 @@ export const collectSliceDefs = (tsIndex: TypeSchemaIndex, flatProfile: Snapshot
                         field.type && !isPrimitiveIdentifier(field.type) ? pyTypeFromIdentifier(field.type) : undefined,
                     elementTypeId: field.type && !isPrimitiveIdentifier(field.type) ? field.type : undefined,
                     isTypeDiscriminated: typeDiscriminated,
-                    typeDiscriminatorResource,
+                    typeDiscriminatorResource: slice.resourceType,
                     nameCandidates: slice.nameCandidates,
                 };
             });
diff --git a/src/api/writer-generator/python/profile-validation.ts b/src/api/writer-generator/python/profile-validation.ts
index 4f9d7988..36af6b50 100644
--- a/src/api/writer-generator/python/profile-validation.ts
+++ b/src/api/writer-generator/python/profile-validation.ts
@@ -128,18 +128,16 @@ const collectRegularFieldValidation = (
             pushListValidation(errorLines, "errors", "validate_reference", [JSON.stringify(pyName)], allowed);
         }
         if (fieldSlicing?.slices) {
-            collectSliceValidation(field, fieldSlicing, pyName, helpers, errorLines, tsIndex, formatName);
+            collectSliceValidation(fieldSlicing, pyName, helpers, errorLines, formatName);
         }
     }
 };
 
 const collectSliceValidation = (
-    field: RegularField | ChoiceFieldInstance,
     fieldSlicing: FieldSlicing,
     name: string,
     helpers: Set<string>,
     errorLines: string[],
-    tsIndex: TypeSchemaIndex,
     formatName: (s: string) => string,
 ): void => {
     if (!fieldSlicing.slices) return;
@@ -154,17 +152,10 @@ const collectSliceValidation = (
                 `errors.extend(validate_slice_cardinality(self._resource, profile_name, ${JSON.stringify(name)}, ${JSON.stringify(match)}, ${JSON.stringify(sliceName)}, ${min}, ${max}))`,
             );
         }
-        // Collect required fields within the slice element
-        const sliceRequiredFields: string[] = [];
-        const matchKeys = new Set(Object.keys(match));
-        for (const rf of slice.required ?? []) {
-            if (!matchKeys.has(rf)) sliceRequiredFields.push(pyFieldName(rf, formatName));
-        }
-        // Constrained choice: the single variant is required
-        if (field.type && slice.elements) {
-            const cc = tsIndex.constrainedChoice(field.type.package, field.type, slice.elements);
-            if (cc) sliceRequiredFields.push(pyFieldName(cc.variant, formatName));
-        }
+        // Required fields within the slice element; for a constrained choice
+        // the single variant is required
+        const sliceRequiredFields = (slice.effectiveRequired ?? []).map((rf) => pyFieldName(rf, formatName));
+        if (slice.constrainedChoice) sliceRequiredFields.push(pyFieldName(slice.constrainedChoice.variant, formatName));
         if (sliceRequiredFields.length > 0) {
             helpers.add("validate_slice_fields");
             pushListValidation(
diff --git a/src/api/writer-generator/typescript/profile-slices.ts b/src/api/writer-generator/typescript/profile-slices.ts
index 188853d4..2e303441 100644
--- a/src/api/writer-generator/typescript/profile-slices.ts
+++ b/src/api/writer-generator/typescript/profile-slices.ts
@@ -1,7 +1,6 @@
 import {
     type ConstrainedChoiceInfo,
     type FieldSlicing,
-    isChoiceDeclarationField,
     isNotChoiceDeclarationField,
     isPrimitiveIdentifier,
     isTypeDiscriminated,
@@ -21,54 +20,24 @@ import {
 import { tsGet, tsTypeFromIdentifier } from "./utils";
 import type { TypeScript } from "./writer";
 
-/** Collect choice declaration field names from a base type schema */
-const collectChoiceBaseNames = (tsIndex: TypeSchemaIndex, typeId: TypeIdentifier): Set<string> => {
-    const names = new Set<string>();
-    const schema = tsIndex.resolveType(typeId);
-    if (schema && "fields" in schema && schema.fields) {
-        for (const [name, f] of Object.entries(schema.fields)) {
-            if (isChoiceDeclarationField(f)) names.add(name);
-        }
-    }
-    return names;
-};
-
-/** Extract resource type name from a type-discriminator match (e.g. {"resource":{"resourceType":"Patient"}} → "Patient") */
-export const extractResourceTypeFromMatch = (match: Record<string, unknown>): string | undefined => {
-    for (const value of Object.values(match)) {
-        if (typeof value !== "object" || value === null) continue;
-        const obj = value as Record<string, unknown>;
-        if (typeof obj.resourceType === "string") return obj.resourceType;
-        const nested = extractResourceTypeFromMatch(obj);
-        if (nested) return nested;
-    }
-    return undefined;
-};
-
 export const collectTypesFromSlices = (
     tsIndex: TypeSchemaIndex,
     snapshot: SnapshotProfileTypeSchema,
     addType: (typeId: TypeIdentifier) => void,
 ) => {
-    const pkgName = snapshot.identifier.package;
     for (const [fieldName, fieldSlicing] of Object.entries(snapshot.slicing ?? {})) {
         const field = snapshot.fields[fieldName];
         if (!isNotChoiceDeclarationField(field) || !fieldSlicing.slices || !field.type) continue;
-        const isTypeDisc = isTypeDiscriminated(fieldSlicing);
         for (const slice of Object.values(fieldSlicing.slices)) {
             if (Object.keys(slice.match ?? {}).length > 0) {
                 addType(field.type);
-                const cc = slice.elements ? tsIndex.constrainedChoice(pkgName, field.type, slice.elements) : undefined;
-                if (cc) addType(cc.variantType);
+                if (slice.constrainedChoice) addType(slice.constrainedChoice.variantType);
                 // For type discriminator slices, also import the matched resource type
-                if (isTypeDisc && slice.match) {
-                    const resourceTypeName = extractResourceTypeFromMatch(slice.match);
-                    if (resourceTypeName) {
-                        const resourceSchema = tsIndex.schemas.find(
-                            (s) => s.identifier.name === resourceTypeName && s.identifier.kind === "resource",
-                        );
-                        if (resourceSchema) addType(resourceSchema.identifier);
-                    }
+                if (slice.resourceType) {
+                    const resourceSchema = tsIndex.schemas.find(
+                        (s) => s.identifier.name === slice.resourceType && s.identifier.kind === "resource",
+                    );
+                    if (resourceSchema) addType(resourceSchema.identifier);
                 }
             }
         }
@@ -87,14 +56,8 @@ export const collectRequiredSliceNames = (
     fieldSlicing: FieldSlicing | undefined,
 ): string[] | undefined => {
     if (!field.array || !fieldSlicing?.slices) return undefined;
-    if (isTypeDiscriminated(fieldSlicing)) return undefined;
     const names = Object.entries(fieldSlicing.slices)
-        .filter(([_, s]) => {
-            if (s.min === undefined || s.min < 1 || !s.match || Object.keys(s.match).length === 0) return false;
-            const matchKeys = new Set(Object.keys(s.match));
-            const requiredBeyondMatch = (s.required ?? []).filter((name) => !matchKeys.has(name));
-            return requiredBeyondMatch.length === 0;
-        })
+        .filter(([_, s]) => s.autoStub)
         .map(([name]) => name);
     return names.length > 0 ? names : undefined;
 };
@@ -119,26 +82,19 @@ export type SliceDef = {
     max: number;
 };
 
-export const collectSliceDefs = (tsIndex: TypeSchemaIndex, snapshot: SnapshotProfileTypeSchema): SliceDef[] =>
+export const collectSliceDefs = (_tsIndex: TypeSchemaIndex, snapshot: SnapshotProfileTypeSchema): SliceDef[] =>
     Object.entries(snapshot.slicing ?? {}).flatMap(([fieldName, fieldSlicing]) => {
         const field = snapshot.fields[fieldName];
         if (!isNotChoiceDeclarationField(field) || !fieldSlicing.slices || !field.type) return [];
         const baseType = tsTypeFromIdentifier(field.type);
-        const pkgName = snapshot.identifier.package;
-        const choiceBaseNames = collectChoiceBaseNames(tsIndex, field.type);
         const isTypeDisc = isTypeDiscriminated(fieldSlicing);
         return Object.entries(fieldSlicing.slices)
             .filter(([_, slice]) => Object.keys(slice.match ?? {}).length > 0)
             .map(([sliceName, slice]) => {
-                const matchFields = Object.keys(slice.match ?? {});
-                const required = (slice.required ?? []).filter(
-                    (name) => !matchFields.includes(name) && !choiceBaseNames.has(name),
-                );
-                const cc = slice.elements ? tsIndex.constrainedChoice(pkgName, field.type, slice.elements) : undefined;
+                const cc = slice.constrainedChoice;
                 // Skip flattening for primitive types — can't intersect object with boolean/string/etc.
                 const constrainedChoice = cc && !isPrimitiveIdentifier(cc.variantType) ? cc : undefined;
-                const resourceType = isTypeDisc ? extractResourceTypeFromMatch(slice.match ?? {}) : undefined;
-                const typedBaseType = resourceType ? `${baseType}<${resourceType}>` : baseType;
+                const typedBaseType = slice.resourceType ? `${baseType}<${slice.resourceType}>` : baseType;
                 return {
                     fieldName,
                     baseType,
@@ -146,7 +102,7 @@ export const collectSliceDefs = (tsIndex: TypeSchemaIndex, snapshot: SnapshotPro
                     sliceName,
                     baseName: slice.nameCandidates.recommended,
                     match: slice.match ?? {},
-                    required,
+                    required: slice.effectiveRequired ?? [],
                     excluded: slice.excluded ?? [],
                     array: Boolean(field.array),
                     constrainedChoice,
diff --git a/src/api/writer-generator/typescript/profile-validation.ts b/src/api/writer-generator/typescript/profile-validation.ts
index 154acc1d..68859bbb 100644
--- a/src/api/writer-generator/typescript/profile-validation.ts
+++ b/src/api/writer-generator/typescript/profile-validation.ts
@@ -18,7 +18,7 @@ export const collectRegularFieldValidation = (
     field: RegularField | ChoiceFieldInstance,
     resolveRef: (ref: TypeIdentifier) => TypeIdentifier,
     canonicalUrlExpr?: { url: string; expr: string },
-    tsIndex?: TypeSchemaIndex,
+    _tsIndex?: TypeSchemaIndex,
     fieldSlicing?: FieldSlicing,
 ) => {
     if (field.excluded) {
@@ -60,17 +60,10 @@ export const collectRegularFieldValidation = (
                     `...validateSliceCardinality(res, profileName, ${JSON.stringify(name)}, ${JSON.stringify(match)}, ${JSON.stringify(sliceName)}, ${min}, ${max})`,
                 );
             }
-            // Collect required fields within the slice element
-            const sliceRequiredFields: string[] = [];
-            const matchKeys = new Set(Object.keys(match));
-            for (const rf of slice.required ?? []) {
-                if (!matchKeys.has(rf)) sliceRequiredFields.push(rf);
-            }
-            // Constrained choice: the single variant is required
-            if (tsIndex && field.type && slice.elements) {
-                const cc = tsIndex.constrainedChoice(field.type.package, field.type, slice.elements);
-                if (cc) sliceRequiredFields.push(cc.variant);
-            }
+            // Required fields within the slice element; for a constrained
+            // choice the single variant is required
+            const sliceRequiredFields = [...(slice.effectiveRequired ?? [])];
+            if (slice.constrainedChoice) sliceRequiredFields.push(slice.constrainedChoice.variant);
             if (sliceRequiredFields.length > 0) {
                 errors.push(
                     `...validateSliceFields(res, profileName, ${JSON.stringify(name)}, ${JSON.stringify(match)}, ${JSON.stringify(sliceName)}, ${JSON.stringify(sliceRequiredFields)})`,
diff --git a/src/typeschema/types.ts b/src/typeschema/types.ts
index f6ed9d45..0b684841 100644
--- a/src/typeschema/types.ts
+++ b/src/typeschema/types.ts
@@ -333,6 +333,17 @@ export interface FieldSlice {
     excluded?: string[];
     elements?: string[];
     nameCandidates: NameCandidates;
+
+    // Derived facts, populated on profile snapshots at snapshot-build time so
+    // writers share one implementation instead of re-deriving them per language.
+    /** `required` minus match keys and choice-declaration base names */
+    effectiveRequired?: string[];
+    /** The single choice variant this slice constrains (e.g. BP component → valueQuantity) */
+    constrainedChoice?: ConstrainedChoiceInfo;
+    /** Slice can be auto-populated with just the discriminator match values */
+    autoStub?: boolean;
+    /** Matched resource type for type-discriminated slices (e.g. Bundle entry → "Patient") */
+    resourceType?: string;
 }
 
 export interface ExtensionSubField {
diff --git a/src/typeschema/utils.ts b/src/typeschema/utils.ts
index acf7081d..2aabfc2d 100644
--- a/src/typeschema/utils.ts
+++ b/src/typeschema/utils.ts
@@ -15,6 +15,7 @@ import {
     type ConstrainedChoiceInfo,
     concatIdentifiers,
     type Field,
+    type FieldSlice,
     type FieldSlicing,
     type GenericParam,
     type Identifier,
@@ -25,12 +26,14 @@ import {
     isLogicalTypeSchema,
     isNestedIdentifier,
     isNestedTypeSchema,
+    isNotChoiceDeclarationField,
     isProfileTypeSchema,
     isResourceIdentifier,
     isResourceTypeSchema,
     isSnapshotProfileIdentifier,
     isSnapshotProfileTypeSchema,
     isSpecializationTypeSchema,
+    isTypeDiscriminated,
     type LogicalIdentifier,
     type LogicalTypeSchema,
     type NestedIdentifier,
@@ -690,6 +693,91 @@ export const mkTypeSchemaIndex = (
         };
     };
 
+    const constrainedChoice = (
+        pkgName: PkgName,
+        baseTypeId: TypeIdentifier,
+        sliceElements: string[],
+    ): ConstrainedChoiceInfo | undefined => {
+        const baseSchema = resolveByUrl(pkgName, baseTypeId.url as CanonicalUrl);
+        if (!baseSchema || !("fields" in baseSchema) || !baseSchema.fields) return undefined;
+        for (const [fieldName, field] of Object.entries(baseSchema.fields)) {
+            if (!isChoiceDeclarationField(field)) continue;
+            const matchingVariants = field.choices.filter((c) => sliceElements.includes(c));
+            if (matchingVariants.length !== 1) continue;
+            const variantName = matchingVariants[0] as string;
+            const variantField = baseSchema.fields[variantName];
+            if (!variantField || !isChoiceInstanceField(variantField)) continue;
+            return {
+                choiceBase: fieldName,
+                variant: variantName,
+                variantType: variantField.type,
+                allChoiceNames: field.choices,
+            };
+        }
+        return undefined;
+    };
+
+    /** Extract the matched resource type from a type-discriminator match (e.g. {"resource":{"resourceType":"Patient"}}) */
+    const extractResourceTypeFromMatch = (match: Record<string, unknown>): string | undefined => {
+        for (const value of Object.values(match)) {
+            if (typeof value !== "object" || value === null) continue;
+            const obj = value as Record<string, unknown>;
+            if (typeof obj.resourceType === "string") return obj.resourceType;
+            const nested = extractResourceTypeFromMatch(obj);
+            if (nested) return nested;
+        }
+        return undefined;
+    };
+
+    /** Populate the derived per-slice facts (effectiveRequired, constrainedChoice,
+     *  autoStub, resourceType) on a snapshot's slicing map. Slices are copied —
+     *  the source profile schemas stay untouched. */
+    const enrichSliceInfo = (
+        slicing: Record<string, FieldSlicing>,
+        fields: Record<string, Field>,
+        pkgName: PkgName,
+    ): Record<string, FieldSlicing> => {
+        const result: Record<string, FieldSlicing> = {};
+        for (const [fieldName, fieldSlicing] of Object.entries(slicing)) {
+            if (!fieldSlicing.slices) {
+                result[fieldName] = fieldSlicing;
+                continue;
+            }
+            const field = fields[fieldName];
+            const fieldType = field && isNotChoiceDeclarationField(field) ? field.type : undefined;
+            const typeSchema = fieldType ? resolveType(fieldType) : undefined;
+            const choiceBaseNames = new Set(
+                typeSchema && "fields" in typeSchema && typeSchema.fields
+                    ? Object.keys(typeSchema.fields).filter((n) => isChoiceDeclarationField(typeSchema.fields?.[n]))
+                    : [],
+            );
+            const typeDisc = isTypeDiscriminated(fieldSlicing);
+            const slices: Record<string, FieldSlice> = {};
+            for (const [sliceName, slice] of Object.entries(fieldSlicing.slices)) {
+                const matchKeys = new Set(Object.keys(slice.match ?? {}));
+                const required = slice.required ?? [];
+                const effectiveRequired = required.filter((n) => !matchKeys.has(n) && !choiceBaseNames.has(n));
+                // Stub eligibility keeps choice-base names: a slice requiring its
+                // choice (e.g. BP component value[x]) needs user data, not a stub.
+                const requiredBeyondMatch = required.filter((n) => !matchKeys.has(n));
+                const autoStub =
+                    !typeDisc && (slice.min ?? 0) >= 1 && matchKeys.size > 0 && requiredBeyondMatch.length === 0;
+                const cc =
+                    fieldType && slice.elements ? constrainedChoice(pkgName, fieldType, slice.elements) : undefined;
+                const resourceType = typeDisc ? extractResourceTypeFromMatch(slice.match ?? {}) : undefined;
+                slices[sliceName] = {
+                    ...slice,
+                    ...(effectiveRequired.length > 0 ? { effectiveRequired } : {}),
+                    ...(cc ? { constrainedChoice: cc } : {}),
+                    ...(autoStub ? { autoStub } : {}),
+                    ...(resourceType ? { resourceType } : {}),
+                };
+            }
+            result[fieldName] = { ...fieldSlicing, slices };
+        }
+        return result;
+    };
+
     const buildProfileSnapshot = (schema: ProfileTypeSchema): SnapshotProfileTypeSchema => {
         const flat = flatProfile(schema);
         const flatFields = flat.fields ?? {};
@@ -735,7 +823,7 @@ export const mkTypeSchemaIndex = (
             base: flat.base,
             description: flat.description,
             fields: flatFields,
-            slicing: flat.slicing,
+            slicing: flat.slicing ? enrichSliceInfo(flat.slicing, flatFields, schema.identifier.package) : undefined,
             inheritedRequiredFields: inheritedRequiredFields.length > 0 ? inheritedRequiredFields : undefined,
             extensions: flat.extensions,
             dependencies: flat.dependencies,
@@ -758,30 +846,6 @@ export const mkTypeSchemaIndex = (
     const collectSnapshotProfiles = (): SnapshotProfileTypeSchema[] =>
         Object.values(snapshotIndex).flatMap((byPkg) => Object.values(byPkg));
 
-    const constrainedChoice = (
-        pkgName: PkgName,
-        baseTypeId: TypeIdentifier,
-        sliceElements: string[],
-    ): ConstrainedChoiceInfo | undefined => {
-        const baseSchema = resolveByUrl(pkgName, baseTypeId.url as CanonicalUrl);
-        if (!baseSchema || !("fields" in baseSchema) || !baseSchema.fields) return undefined;
-        for (const [fieldName, field] of Object.entries(baseSchema.fields)) {
-            if (!isChoiceDeclarationField(field)) continue;
-            const matchingVariants = field.choices.filter((c) => sliceElements.includes(c));
-            if (matchingVariants.length !== 1) continue;
-            const variantName = matchingVariants[0] as string;
-            const variantField = baseSchema.fields[variantName];
-            if (!variantField || !isChoiceInstanceField(variantField)) continue;
-            return {
-                choiceBase: fieldName,
-                variant: variantName,
-                variantType: variantField.type,
-                allChoiceNames: field.choices,
-            };
-        }
-        return undefined;
-    };
-
     const isWithMetaField = (profile: ProfileTypeSchema | SnapshotProfileTypeSchema): boolean => {
         const genealogy = tryHierarchy(profile);
         if (!genealogy) return false;

From 7864d2a67ae9f024c2333549d280576960cc96a2 Mon Sep 17 00:00:00 2001
From: Aleksandr Penskoi <alexandr.penskoi@health-samurai.io>
Date: Fri, 24 Jul 2026 16:05:03 +0400
Subject: [PATCH 2/9] test: update snapshots for derived slice facts

---
 .../__snapshots__/introspection.test.ts.snap              | 3 ++-
 .../api/write-generator/__snapshots__/python.test.ts.snap | 8 ++++----
 .../write-generator/__snapshots__/typescript.test.ts.snap | 6 +++---
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/test/api/write-generator/__snapshots__/introspection.test.ts.snap b/test/api/write-generator/__snapshots__/introspection.test.ts.snap
index 6fb1829b..db0dc027 100644
--- a/test/api/write-generator/__snapshots__/introspection.test.ts.snap
+++ b/test/api/write-generator/__snapshots__/introspection.test.ts.snap
@@ -3163,7 +3163,8 @@ exports[`IntrospectionWriter - flat profile output Check bodyweight flat profile
               "CategoryVSCatSlice"
             ],
             "recommended": "VSCat"
-          }
+          },
+          "autoStub": true
         }
       }
     }
diff --git a/test/api/write-generator/__snapshots__/python.test.ts.snap b/test/api/write-generator/__snapshots__/python.test.ts.snap
index 98e4389a..60c4b3c4 100644
--- a/test/api/write-generator/__snapshots__/python.test.ts.snap
+++ b/test/api/write-generator/__snapshots__/python.test.ts.snap
@@ -1922,7 +1922,7 @@ class UscoreRaceExtension:
 
     @classmethod
     def create_resource(cls, *, extension: list[Extension] | None = None) -> Extension:
-        extension_with_defaults = ensure_slice_defaults(list(extension or []), cls._text_slice_match)
+        extension_with_defaults = list(extension or [])
 
         return build_resource(Extension, url="http://hl7.org/fhir/us/core/StructureDefinition/us-core-race", extension=extension_with_defaults)
 
@@ -2092,16 +2092,16 @@ class UscoreRaceExtension:
         errors.extend(validate_slice_cardinality(self._resource, profile_name, "extension", {"url":"ombCategory"}, "ombCategory", 0, 6))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"ombCategory"}, "ombCategory", [
-                "value","valueCoding"
+                "valueCoding"
         ]))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"detailed"}, "detailed", [
-                "value","valueCoding"
+                "valueCoding"
         ]))
         errors.extend(validate_slice_cardinality(self._resource, profile_name, "extension", {"url":"text"}, "text", 1, 1))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"text"}, "text", [
-                "value","valueString"
+                "valueString"
         ]))
         errors.extend(validate_required(self._resource, profile_name, "url"))
         errors.extend(validate_fixed_value(self._resource, profile_name, "url", "http://hl7.org/fhir/us/core/StructureDefinition/us-core-race"))
diff --git a/test/api/write-generator/__snapshots__/typescript.test.ts.snap b/test/api/write-generator/__snapshots__/typescript.test.ts.snap
index ea68c285..86948369 100644
--- a/test/api/write-generator/__snapshots__/typescript.test.ts.snap
+++ b/test/api/write-generator/__snapshots__/typescript.test.ts.snap
@@ -2362,10 +2362,10 @@ export class USCoreRaceExtensionProfile {
             errors: [
                 ...validateRequired(res, profileName, "extension"),
                 ...validateSliceCardinality(res, profileName, "extension", {"url":"ombCategory"}, "ombCategory", 0, 6),
-                ...validateSliceFields(res, profileName, "extension", {"url":"ombCategory"}, "ombCategory", ["value","valueCoding"]),
-                ...validateSliceFields(res, profileName, "extension", {"url":"detailed"}, "detailed", ["value","valueCoding"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"ombCategory"}, "ombCategory", ["valueCoding"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"detailed"}, "detailed", ["valueCoding"]),
                 ...validateSliceCardinality(res, profileName, "extension", {"url":"text"}, "text", 1, 1),
-                ...validateSliceFields(res, profileName, "extension", {"url":"text"}, "text", ["value","valueString"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"text"}, "text", ["valueString"]),
                 ...validateRequired(res, profileName, "url"),
                 ...validateFixedValue(res, profileName, "url", USCoreRaceExtensionProfile.canonicalUrl),
             ],

From 361debb9493e7c441b67b9618777e02aac6f3324 Mon Sep 17 00:00:00 2001
From: Aleksandr Penskoi <alexandr.penskoi@health-samurai.io>
Date: Fri, 24 Jul 2026 16:05:03 +0400
Subject: [PATCH 3/9] chore(examples): regenerate US Core extension profiles

---
 .../profiles/extension_nationality.py         | 20 ++++++++++++++-----
 .../extension_uscore_ethnicity_extension.py   |  8 ++++----
 .../extension_uscore_race_extension.py        |  8 ++++----
 ...ion_uscore_tribal_affiliation_extension.py |  6 +++---
 .../Extension_USCoreEthnicityExtension.ts     |  6 +++---
 .../profiles/Extension_USCoreRaceExtension.ts |  6 +++---
 ...ension_USCoreTribalAffiliationExtension.ts |  4 ++--
 7 files changed, 34 insertions(+), 24 deletions(-)

diff --git a/examples/python-r4-us-core/fhir_types/hl7_fhir_r4_core/profiles/extension_nationality.py b/examples/python-r4-us-core/fhir_types/hl7_fhir_r4_core/profiles/extension_nationality.py
index a218df20..20fb412f 100644
--- a/examples/python-r4-us-core/fhir_types/hl7_fhir_r4_core/profiles/extension_nationality.py
+++ b/examples/python-r4-us-core/fhir_types/hl7_fhir_r4_core/profiles/extension_nationality.py
@@ -10,7 +10,8 @@
 from fhir_types.hl7_fhir_r4_core.base import Extension
 from fhir_types.hl7_fhir_r4_core.base import CodeableConcept, Period
 from fhir_types.profile_helpers import (
-    _get_key, build_resource, get_extension_value, is_extension, push_extension, validate_fixed_value, validate_required
+    _get_key, build_resource, ensure_slice_defaults, get_extension_value, is_extension, push_extension, validate_fixed_value, \
+    validate_required
 )
 
 
@@ -38,16 +39,25 @@ def apply(cls, resource: Extension) -> "NationalityExtension":
         return cls(resource)
 
     @classmethod
-    def create_resource(cls) -> Extension:
-        return build_resource(Extension, url="http://hl7.org/fhir/StructureDefinition/patient-nationality")
+    def create_resource(cls, *, extension: list[Extension] | None = None) -> Extension:
+        extension_with_defaults = list(extension or [])
+
+        return build_resource(Extension, url="http://hl7.org/fhir/StructureDefinition/patient-nationality", extension=extension_with_defaults)
 
     @classmethod
-    def create(cls) -> "NationalityExtension":
-        return cls.apply(cls.create_resource())
+    def create(cls, *, extension: list[Extension] | None = None) -> "NationalityExtension":
+        return cls.apply(cls.create_resource(extension=extension))
 
     def to_resource(self) -> Extension:
         return self._resource
 
+    def get_extension(self) -> list[Extension] | None:
+        return cast('list[Extension] | None', getattr(self._resource, "extension", None))
+
+    def set_extension(self, value: list[Extension]) -> "NationalityExtension":
+        setattr(self._resource, "extension", value)
+        return self
+
     def get_url(self) -> str | None:
         return cast('str | None', getattr(self._resource, "url", None))
 
diff --git a/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_ethnicity_extension.py b/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_ethnicity_extension.py
index df04873c..26a284b4 100644
--- a/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_ethnicity_extension.py
+++ b/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_ethnicity_extension.py
@@ -47,7 +47,7 @@ def apply(cls, resource: Extension) -> "UscoreEthnicityExtension":
 
     @classmethod
     def create_resource(cls, *, extension: list[Extension] | None = None) -> Extension:
-        extension_with_defaults = ensure_slice_defaults(list(extension or []), cls._text_slice_match)
+        extension_with_defaults = list(extension or [])
 
         return build_resource(Extension, url="http://hl7.org/fhir/us/core/StructureDefinition/us-core-ethnicity", extension=extension_with_defaults)
 
@@ -217,16 +217,16 @@ def validate(self) -> dict[str, list[str]]:
         errors.extend(validate_slice_cardinality(self._resource, profile_name, "extension", {"url":"ombCategory"}, "ombCategory", 0, 1))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"ombCategory"}, "ombCategory", [
-                "value","valueCoding"
+                "valueCoding"
         ]))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"detailed"}, "detailed", [
-                "value","valueCoding"
+                "valueCoding"
         ]))
         errors.extend(validate_slice_cardinality(self._resource, profile_name, "extension", {"url":"text"}, "text", 1, 1))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"text"}, "text", [
-                "value","valueString"
+                "valueString"
         ]))
         errors.extend(validate_required(self._resource, profile_name, "url"))
         errors.extend(validate_fixed_value(self._resource, profile_name, "url", "http://hl7.org/fhir/us/core/StructureDefinition/us-core-ethnicity"))
diff --git a/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_race_extension.py b/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_race_extension.py
index 34bb4b32..eec33d8d 100644
--- a/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_race_extension.py
+++ b/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_race_extension.py
@@ -50,7 +50,7 @@ def apply(cls, resource: Extension) -> "UscoreRaceExtension":
 
     @classmethod
     def create_resource(cls, *, extension: list[Extension] | None = None) -> Extension:
-        extension_with_defaults = ensure_slice_defaults(list(extension or []), cls._text_slice_match)
+        extension_with_defaults = list(extension or [])
 
         return build_resource(Extension, url="http://hl7.org/fhir/us/core/StructureDefinition/us-core-race", extension=extension_with_defaults)
 
@@ -220,16 +220,16 @@ def validate(self) -> dict[str, list[str]]:
         errors.extend(validate_slice_cardinality(self._resource, profile_name, "extension", {"url":"ombCategory"}, "ombCategory", 0, 6))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"ombCategory"}, "ombCategory", [
-                "value","valueCoding"
+                "valueCoding"
         ]))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"detailed"}, "detailed", [
-                "value","valueCoding"
+                "valueCoding"
         ]))
         errors.extend(validate_slice_cardinality(self._resource, profile_name, "extension", {"url":"text"}, "text", 1, 1))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"text"}, "text", [
-                "value","valueString"
+                "valueString"
         ]))
         errors.extend(validate_required(self._resource, profile_name, "url"))
         errors.extend(validate_fixed_value(self._resource, profile_name, "url", "http://hl7.org/fhir/us/core/StructureDefinition/us-core-race"))
diff --git a/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_tribal_affiliation_extension.py b/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_tribal_affiliation_extension.py
index de5dc3c9..0467395b 100644
--- a/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_tribal_affiliation_extension.py
+++ b/examples/python-r4-us-core/fhir_types/hl7_fhir_us_core/profiles/extension_uscore_tribal_affiliation_extension.py
@@ -43,7 +43,7 @@ def apply(cls, resource: Extension) -> "UscoreTribalAffiliationExtension":
 
     @classmethod
     def create_resource(cls, *, extension: list[Extension] | None = None) -> Extension:
-        extension_with_defaults = ensure_slice_defaults(list(extension or []), cls._tribal_affiliation_slice_match)
+        extension_with_defaults = list(extension or [])
 
         return build_resource(Extension, url="http://hl7.org/fhir/us/core/StructureDefinition/us-core-tribal-affiliation", extension=extension_with_defaults)
 
@@ -167,12 +167,12 @@ def validate(self) -> dict[str, list[str]]:
         errors.extend(validate_slice_cardinality(self._resource, profile_name, "extension", {"url":"tribalAffiliation"}, "tribalAffiliation", 1, 1))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"tribalAffiliation"}, "tribalAffiliation", [
-                "value","valueCodeableConcept"
+                "valueCodeableConcept"
         ]))
         errors.extend(validate_slice_cardinality(self._resource, profile_name, "extension", {"url":"isEnrolled"}, "isEnrolled", 0, 1))
         errors.extend(
             validate_slice_fields(self._resource, profile_name, "extension", {"url":"isEnrolled"}, "isEnrolled", [
-                "value","valueBoolean"
+                "valueBoolean"
         ]))
         errors.extend(validate_required(self._resource, profile_name, "url"))
         errors.extend(validate_fixed_value(self._resource, profile_name, "url", "http://hl7.org/fhir/us/core/StructureDefinition/us-core-tribal-affiliation"))
diff --git a/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreEthnicityExtension.ts b/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreEthnicityExtension.ts
index 02d37f75..7e5a2339 100644
--- a/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreEthnicityExtension.ts
+++ b/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreEthnicityExtension.ts
@@ -254,10 +254,10 @@ export class USCoreEthnicityExtensionProfile {
             errors: [
                 ...validateRequired(res, profileName, "extension"),
                 ...validateSliceCardinality(res, profileName, "extension", {"url":"ombCategory"}, "ombCategory", 0, 1),
-                ...validateSliceFields(res, profileName, "extension", {"url":"ombCategory"}, "ombCategory", ["value","valueCoding"]),
-                ...validateSliceFields(res, profileName, "extension", {"url":"detailed"}, "detailed", ["value","valueCoding"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"ombCategory"}, "ombCategory", ["valueCoding"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"detailed"}, "detailed", ["valueCoding"]),
                 ...validateSliceCardinality(res, profileName, "extension", {"url":"text"}, "text", 1, 1),
-                ...validateSliceFields(res, profileName, "extension", {"url":"text"}, "text", ["value","valueString"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"text"}, "text", ["valueString"]),
                 ...validateRequired(res, profileName, "url"),
                 ...validateFixedValue(res, profileName, "url", USCoreEthnicityExtensionProfile.canonicalUrl),
             ],
diff --git a/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreRaceExtension.ts b/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreRaceExtension.ts
index 3b342f17..f74623a4 100644
--- a/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreRaceExtension.ts
+++ b/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreRaceExtension.ts
@@ -254,10 +254,10 @@ export class USCoreRaceExtensionProfile {
             errors: [
                 ...validateRequired(res, profileName, "extension"),
                 ...validateSliceCardinality(res, profileName, "extension", {"url":"ombCategory"}, "ombCategory", 0, 6),
-                ...validateSliceFields(res, profileName, "extension", {"url":"ombCategory"}, "ombCategory", ["value","valueCoding"]),
-                ...validateSliceFields(res, profileName, "extension", {"url":"detailed"}, "detailed", ["value","valueCoding"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"ombCategory"}, "ombCategory", ["valueCoding"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"detailed"}, "detailed", ["valueCoding"]),
                 ...validateSliceCardinality(res, profileName, "extension", {"url":"text"}, "text", 1, 1),
-                ...validateSliceFields(res, profileName, "extension", {"url":"text"}, "text", ["value","valueString"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"text"}, "text", ["valueString"]),
                 ...validateRequired(res, profileName, "url"),
                 ...validateFixedValue(res, profileName, "url", USCoreRaceExtensionProfile.canonicalUrl),
             ],
diff --git a/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreTribalAffiliationExtension.ts b/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreTribalAffiliationExtension.ts
index af73bcca..6a0b749d 100644
--- a/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreTribalAffiliationExtension.ts
+++ b/examples/typescript-r4-us-core/fhir-types/hl7-fhir-us-core/profiles/Extension_USCoreTribalAffiliationExtension.ts
@@ -209,9 +209,9 @@ export class USCoreTribalAffiliationExtensionProfile {
             errors: [
                 ...validateRequired(res, profileName, "extension"),
                 ...validateSliceCardinality(res, profileName, "extension", {"url":"tribalAffiliation"}, "tribalAffiliation", 1, 1),
-                ...validateSliceFields(res, profileName, "extension", {"url":"tribalAffiliation"}, "tribalAffiliation", ["value","valueCodeableConcept"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"tribalAffiliation"}, "tribalAffiliation", ["valueCodeableConcept"]),
                 ...validateSliceCardinality(res, profileName, "extension", {"url":"isEnrolled"}, "isEnrolled", 0, 1),
-                ...validateSliceFields(res, profileName, "extension", {"url":"isEnrolled"}, "isEnrolled", ["value","valueBoolean"]),
+                ...validateSliceFields(res, profileName, "extension", {"url":"isEnrolled"}, "isEnrolled", ["valueBoolean"]),
                 ...validateRequired(res, profileName, "url"),
                 ...validateFixedValue(res, profileName, "url", USCoreTribalAffiliationExtensionProfile.canonicalUrl),
             ],

From 22a5c3b6756918a37e604c12bde102ceae2cadfd Mon Sep 17 00:00:00 2001
From: Aleksandr Penskoi <alexandr.penskoi@health-samurai.io>
Date: Fri, 24 Jul 2026 18:09:15 +0400
Subject: [PATCH 4/9] ref: extract per-slice enrichment into enrichSlice helper

---
 src/typeschema/utils.ts | 64 +++++++++++++++++++++++++----------------
 1 file changed, 40 insertions(+), 24 deletions(-)

diff --git a/src/typeschema/utils.ts b/src/typeschema/utils.ts
index 2aabfc2d..f6b7b0f2 100644
--- a/src/typeschema/utils.ts
+++ b/src/typeschema/utils.ts
@@ -729,9 +729,38 @@ export const mkTypeSchemaIndex = (
         return undefined;
     };
 
+    type SliceEnrichmentContext = {
+        pkgName: PkgName;
+        fieldType: TypeIdentifier | undefined;
+        choiceBaseNames: Set<string>;
+        typeDiscriminated: boolean;
+    };
+
+    /** Compute the derived facts for one slice; returns a copy — the source
+     *  profile schemas stay untouched. */
+    const enrichSlice = (slice: FieldSlice, ctx: SliceEnrichmentContext): FieldSlice => {
+        const matchKeys = new Set(Object.keys(slice.match ?? {}));
+        const required = slice.required ?? [];
+        const effectiveRequired = required.filter((n) => !matchKeys.has(n) && !ctx.choiceBaseNames.has(n));
+        // Stub eligibility keeps choice-base names: a slice requiring its
+        // choice (e.g. BP component value[x]) needs user data, not a stub.
+        const requiredBeyondMatch = required.filter((n) => !matchKeys.has(n));
+        const autoStub =
+            !ctx.typeDiscriminated && (slice.min ?? 0) >= 1 && matchKeys.size > 0 && requiredBeyondMatch.length === 0;
+        const cc =
+            ctx.fieldType && slice.elements ? constrainedChoice(ctx.pkgName, ctx.fieldType, slice.elements) : undefined;
+        const resourceType = ctx.typeDiscriminated ? extractResourceTypeFromMatch(slice.match ?? {}) : undefined;
+        return {
+            ...slice,
+            ...(effectiveRequired.length > 0 ? { effectiveRequired } : {}),
+            ...(cc ? { constrainedChoice: cc } : {}),
+            ...(autoStub ? { autoStub } : {}),
+            ...(resourceType ? { resourceType } : {}),
+        };
+    };
+
     /** Populate the derived per-slice facts (effectiveRequired, constrainedChoice,
-     *  autoStub, resourceType) on a snapshot's slicing map. Slices are copied —
-     *  the source profile schemas stay untouched. */
+     *  autoStub, resourceType) on a snapshot's slicing map. */
     const enrichSliceInfo = (
         slicing: Record<string, FieldSlicing>,
         fields: Record<string, Field>,
@@ -751,28 +780,15 @@ export const mkTypeSchemaIndex = (
                     ? Object.keys(typeSchema.fields).filter((n) => isChoiceDeclarationField(typeSchema.fields?.[n]))
                     : [],
             );
-            const typeDisc = isTypeDiscriminated(fieldSlicing);
-            const slices: Record<string, FieldSlice> = {};
-            for (const [sliceName, slice] of Object.entries(fieldSlicing.slices)) {
-                const matchKeys = new Set(Object.keys(slice.match ?? {}));
-                const required = slice.required ?? [];
-                const effectiveRequired = required.filter((n) => !matchKeys.has(n) && !choiceBaseNames.has(n));
-                // Stub eligibility keeps choice-base names: a slice requiring its
-                // choice (e.g. BP component value[x]) needs user data, not a stub.
-                const requiredBeyondMatch = required.filter((n) => !matchKeys.has(n));
-                const autoStub =
-                    !typeDisc && (slice.min ?? 0) >= 1 && matchKeys.size > 0 && requiredBeyondMatch.length === 0;
-                const cc =
-                    fieldType && slice.elements ? constrainedChoice(pkgName, fieldType, slice.elements) : undefined;
-                const resourceType = typeDisc ? extractResourceTypeFromMatch(slice.match ?? {}) : undefined;
-                slices[sliceName] = {
-                    ...slice,
-                    ...(effectiveRequired.length > 0 ? { effectiveRequired } : {}),
-                    ...(cc ? { constrainedChoice: cc } : {}),
-                    ...(autoStub ? { autoStub } : {}),
-                    ...(resourceType ? { resourceType } : {}),
-                };
-            }
+            const ctx: SliceEnrichmentContext = {
+                pkgName,
+                fieldType,
+                choiceBaseNames,
+                typeDiscriminated: isTypeDiscriminated(fieldSlicing),
+            };
+            const slices = Object.fromEntries(
+                Object.entries(fieldSlicing.slices).map(([sliceName, slice]) => [sliceName, enrichSlice(slice, ctx)]),
+            );
             result[fieldName] = { ...fieldSlicing, slices };
         }
         return result;

From 4d87fe5dc3069bf2cc8bb99139af59e51b6cb607 Mon Sep 17 00:00:00 2001
From: Aleksandr Penskoi <alexandr.penskoi@health-samurai.io>
Date: Fri, 24 Jul 2026 18:10:36 +0400
Subject: [PATCH 5/9] test(typeschema): cover derived slice fact enrichment

---
 test/unit/typeschema/slice-enrichment.test.ts | 125 ++++++++++++++++++
 1 file changed, 125 insertions(+)
 create mode 100644 test/unit/typeschema/slice-enrichment.test.ts

diff --git a/test/unit/typeschema/slice-enrichment.test.ts b/test/unit/typeschema/slice-enrichment.test.ts
new file mode 100644
index 00000000..93b9d8f1
--- /dev/null
+++ b/test/unit/typeschema/slice-enrichment.test.ts
@@ -0,0 +1,125 @@
+import { describe, expect, it } from "bun:test";
+import { mkTypeSchemaIndex } from "@root/typeschema/utils";
+import type { CanonicalUrl, TypeSchema } from "@typeschema/types";
+import { mkErrorLogger, mkR4Register, r4Package, registerFs, resolveTs } from "@typeschema-test/utils";
+
+const myPkg = { name: "mypackage", version: "0.0.0" };
+
+/** Derived slice facts (effectiveRequired, constrainedChoice, autoStub,
+ *  resourceType) are computed once at snapshot build by enrichSliceInfo. */
+describe("slice enrichment on profile snapshots", async () => {
+    const r4 = await mkR4Register();
+    const logger = mkErrorLogger();
+
+    registerFs(r4, {
+        url: "http://example.org/StructureDefinition/TestVitals",
+        name: "TestVitals",
+        base: "http://hl7.org/fhir/StructureDefinition/Observation",
+        derivation: "constraint",
+        kind: "resource",
+        elements: {
+            category: {
+                type: "CodeableConcept",
+                array: true,
+                slicing: {
+                    discriminator: [{ type: "pattern", path: "$this" }],
+                    rules: "open",
+                    slices: {
+                        VSCat: { min: 1, max: 1, match: { coding: [{ code: "vital-signs" }] } },
+                    },
+                },
+            },
+            component: {
+                array: true,
+                slicing: {
+                    discriminator: [{ type: "pattern", path: "code" }],
+                    rules: "open",
+                    slices: {
+                        Sys: {
+                            min: 1,
+                            max: 1,
+                            match: { code: { coding: [{ code: "8480-6" }] } },
+                            schema: {
+                                required: ["value"],
+                                elements: { code: {}, valueQuantity: {} },
+                            },
+                        },
+                    },
+                },
+            },
+        },
+    });
+
+    registerFs(r4, {
+        url: "http://example.org/StructureDefinition/TestBundle",
+        name: "TestBundle",
+        base: "http://hl7.org/fhir/StructureDefinition/Bundle",
+        derivation: "constraint",
+        kind: "resource",
+        elements: {
+            entry: {
+                array: true,
+                slicing: {
+                    discriminator: [{ type: "type", path: "resource" }],
+                    rules: "open",
+                    slices: {
+                        Pat: {
+                            min: 1,
+                            max: 1,
+                            match: { resource: { resourceType: "Patient" } } as Record<string, unknown>,
+                        },
+                    },
+                },
+            },
+        },
+    });
+
+    const schemas: TypeSchema[] = [];
+    for (const [pkg, url] of [
+        [myPkg, "http://example.org/StructureDefinition/TestVitals"],
+        [myPkg, "http://example.org/StructureDefinition/TestBundle"],
+        [r4Package, "http://hl7.org/fhir/StructureDefinition/Observation"],
+        [r4Package, "http://hl7.org/fhir/StructureDefinition/Bundle"],
+        [r4Package, "http://hl7.org/fhir/StructureDefinition/DomainResource"],
+        [r4Package, "http://hl7.org/fhir/StructureDefinition/Resource"],
+    ] as const) {
+        schemas.push(...(await resolveTs(r4, pkg, url as CanonicalUrl, logger)));
+    }
+    const tsIndex = mkTypeSchemaIndex(schemas, { register: r4, logger });
+
+    const snapshot = (name: string) => {
+        const snap = tsIndex.collectSnapshotProfiles().find((s) => s.identifier.name === name);
+        if (!snap) throw new Error(`No snapshot for ${name}`);
+        return snap;
+    };
+
+    it("marks match-only required slices as autoStub", () => {
+        const slice = snapshot("TestVitals").slicing?.category?.slices?.VSCat;
+        expect(slice?.autoStub).toBeTrue();
+        expect(slice?.effectiveRequired).toBeUndefined();
+        expect(slice?.constrainedChoice).toBeUndefined();
+        expect(slice?.resourceType).toBeUndefined();
+    });
+
+    it("resolves constrained choices and keeps the autoStub/effectiveRequired asymmetry", () => {
+        const slice = snapshot("TestVitals").slicing?.component?.slices?.Sys;
+        // The slice narrows component.value[x] to valueQuantity.
+        expect(slice?.constrainedChoice?.choiceBase).toBe("value");
+        expect(slice?.constrainedChoice?.variant).toBe("valueQuantity");
+        expect(String(slice?.constrainedChoice?.variantType.name)).toBe("Quantity");
+        // "value" is a choice-declaration base name, never a real JSON key:
+        // it is dropped from effectiveRequired (validation must not check it) …
+        expect(slice?.effectiveRequired).toBeUndefined();
+        // … but it still blocks auto-stubbing — the slice needs user data
+        // (a valueQuantity), so a match-only stub would be invalid.
+        expect(slice?.autoStub).toBeUndefined();
+    });
+
+    it("extracts the resource type for type-discriminated slices", () => {
+        const slice = snapshot("TestBundle").slicing?.entry?.slices?.Pat;
+        expect(slice?.resourceType).toBe("Patient");
+        // Type-discriminated slices are never auto-stubbed: the stub would
+        // only set resourceType, the user must provide the typed resource.
+        expect(slice?.autoStub).toBeUndefined();
+    });
+});

From fa5e34e3fee59bf3e61093679fe1bcb26d9328a2 Mon Sep 17 00:00:00 2001
From: Aleksandr Penskoi <alexandr.penskoi@health-samurai.io>
Date: Fri, 24 Jul 2026 18:17:45 +0400
Subject: [PATCH 6/9] feat(typeschema): model slice match as a discriminated
 SliceMatch union
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

FieldSlice.match becomes { kind: "value" | "type", value } — the runtime
discriminator values keep their shape under 'value', while 'kind' states
whether they are fixed/pattern discriminator values or a resource-type
discriminator. Empty matches are no longer stored, so consumers test presence
instead of key-counting. Generated output is unchanged.
---
 src/api/writer-generator/python/profile-slices.ts |  4 ++--
 .../writer-generator/python/profile-validation.ts |  4 ++--
 .../writer-generator/typescript/profile-slices.ts |  6 +++---
 .../typescript/profile-validation.ts              |  4 ++--
 src/typeschema/core/field-builder.ts              | 10 +++++++---
 src/typeschema/types.ts                           | 12 +++++++++++-
 src/typeschema/utils.ts                           |  4 ++--
 .../__snapshots__/introspection.test.ts.snap      | 15 +++++++++------
 8 files changed, 38 insertions(+), 21 deletions(-)

diff --git a/src/api/writer-generator/python/profile-slices.ts b/src/api/writer-generator/python/profile-slices.ts
index cf348984..207992ef 100644
--- a/src/api/writer-generator/python/profile-slices.ts
+++ b/src/api/writer-generator/python/profile-slices.ts
@@ -97,7 +97,7 @@ export const collectSliceDefs = (tsIndex: TypeSchemaIndex, flatProfile: Snapshot
         const baseSchema = tsIndex.resolveType(field.type);
         const typeDiscriminated = isTypeDiscriminated(fieldSlicing);
         return Object.entries(fieldSlicing.slices)
-            .filter(([_, slice]) => Object.keys(slice.match ?? {}).length > 0)
+            .filter(([_, slice]) => slice.match !== undefined)
             .map(([sliceName, slice]) => {
                 const cc = slice.constrainedChoice;
                 // Skip flattening for primitive types — can't wrap/unwrap under a variant key.
@@ -105,7 +105,7 @@ export const collectSliceDefs = (tsIndex: TypeSchemaIndex, flatProfile: Snapshot
                 return {
                     fieldName,
                     sliceName,
-                    match: normalizeMatchForPython(tsIndex, slice.match ?? {}, baseSchema),
+                    match: normalizeMatchForPython(tsIndex, slice.match?.value ?? {}, baseSchema),
                     required: slice.effectiveRequired ?? [],
                     array: Boolean(field.array),
                     max: slice.max ?? 0,
diff --git a/src/api/writer-generator/python/profile-validation.ts b/src/api/writer-generator/python/profile-validation.ts
index 36af6b50..5ff24961 100644
--- a/src/api/writer-generator/python/profile-validation.ts
+++ b/src/api/writer-generator/python/profile-validation.ts
@@ -142,8 +142,8 @@ const collectSliceValidation = (
 ): void => {
     if (!fieldSlicing.slices) return;
     for (const [sliceName, slice] of Object.entries(fieldSlicing.slices)) {
-        const match = slice.match ?? {};
-        if (Object.keys(match).length === 0) continue;
+        const match = slice.match?.value;
+        if (!match) continue;
         if (slice.min !== undefined || slice.max !== undefined) {
             const min = slice.min ?? 0;
             const max = slice.max ?? 0;
diff --git a/src/api/writer-generator/typescript/profile-slices.ts b/src/api/writer-generator/typescript/profile-slices.ts
index 2e303441..758f825c 100644
--- a/src/api/writer-generator/typescript/profile-slices.ts
+++ b/src/api/writer-generator/typescript/profile-slices.ts
@@ -29,7 +29,7 @@ export const collectTypesFromSlices = (
         const field = snapshot.fields[fieldName];
         if (!isNotChoiceDeclarationField(field) || !fieldSlicing.slices || !field.type) continue;
         for (const slice of Object.values(fieldSlicing.slices)) {
-            if (Object.keys(slice.match ?? {}).length > 0) {
+            if (slice.match !== undefined) {
                 addType(field.type);
                 if (slice.constrainedChoice) addType(slice.constrainedChoice.variantType);
                 // For type discriminator slices, also import the matched resource type
@@ -89,7 +89,7 @@ export const collectSliceDefs = (_tsIndex: TypeSchemaIndex, snapshot: SnapshotPr
         const baseType = tsTypeFromIdentifier(field.type);
         const isTypeDisc = isTypeDiscriminated(fieldSlicing);
         return Object.entries(fieldSlicing.slices)
-            .filter(([_, slice]) => Object.keys(slice.match ?? {}).length > 0)
+            .filter(([_, slice]) => slice.match !== undefined)
             .map(([sliceName, slice]) => {
                 const cc = slice.constrainedChoice;
                 // Skip flattening for primitive types — can't intersect object with boolean/string/etc.
@@ -101,7 +101,7 @@ export const collectSliceDefs = (_tsIndex: TypeSchemaIndex, snapshot: SnapshotPr
                     typedBaseType,
                     sliceName,
                     baseName: slice.nameCandidates.recommended,
-                    match: slice.match ?? {},
+                    match: slice.match?.value ?? {},
                     required: slice.effectiveRequired ?? [],
                     excluded: slice.excluded ?? [],
                     array: Boolean(field.array),
diff --git a/src/api/writer-generator/typescript/profile-validation.ts b/src/api/writer-generator/typescript/profile-validation.ts
index 68859bbb..b10090e5 100644
--- a/src/api/writer-generator/typescript/profile-validation.ts
+++ b/src/api/writer-generator/typescript/profile-validation.ts
@@ -51,8 +51,8 @@ export const collectRegularFieldValidation = (
 
     if (fieldSlicing?.slices) {
         for (const [sliceName, slice] of Object.entries(fieldSlicing.slices)) {
-            const match = slice.match ?? {};
-            if (Object.keys(match).length === 0) continue;
+            const match = slice.match?.value;
+            if (!match) continue;
             if (slice.min !== undefined || slice.max !== undefined) {
                 const min = slice.min ?? 0;
                 const max = slice.max ?? 0;
diff --git a/src/typeschema/core/field-builder.ts b/src/typeschema/core/field-builder.ts
index d0182e41..c3b91736 100644
--- a/src/typeschema/core/field-builder.ts
+++ b/src/typeschema/core/field-builder.ts
@@ -20,6 +20,7 @@ import type {
     ProfileIdentifier,
     RegularField,
     RichFHIRSchema,
+    SliceMatch,
     TypeIdentifier,
     ValueConstraint,
 } from "../types";
@@ -294,16 +295,19 @@ export const buildSlicing = (fieldName: string, element: FHIRSchemaElement): Fie
     const slicing = element.slicing;
     if (!slicing) return undefined;
 
+    const matchKind: SliceMatch["kind"] = slicing.discriminator?.some((d) => d.type === "type") ? "type" : "value";
     const slices: Record<string, FieldSlice> = {};
     for (const [name, slice] of Object.entries(slicing.slices ?? {})) {
         if (!slice) continue;
         const { required, excluded, elements } = slice.schema ? extractSliceFieldNames(slice.schema) : {};
+        const matchValue = isEmptyMatch(slice.match)
+            ? computeMatchFromSchema(slicing.discriminator ?? [], slice.schema)
+            : (slice.match as Record<string, unknown> | undefined);
         slices[name] = {
             min: slice.min,
             max: slice.max,
-            match: isEmptyMatch(slice.match)
-                ? computeMatchFromSchema(slicing.discriminator ?? [], slice.schema)
-                : (slice.match as Record<string, unknown> | undefined),
+            match:
+                matchValue && Object.keys(matchValue).length > 0 ? { kind: matchKind, value: matchValue } : undefined,
             required,
             excluded,
             elements,
diff --git a/src/typeschema/types.ts b/src/typeschema/types.ts
index 0b684841..5fbc41f5 100644
--- a/src/typeschema/types.ts
+++ b/src/typeschema/types.ts
@@ -325,10 +325,20 @@ export type NameCandidates = {
     recommended: string;
 };
 
+/** How a slice is recognized in instance data. `value` holds the discriminator
+ *  values keyed by element name and is used verbatim for runtime matching;
+ *  `kind` says where those values come from — fixed/pattern discriminator
+ *  values (`"value"`) or a resource-type discriminator (`"type"`, e.g.
+ *  Bundle.entry sliced by entry.resource resourceType). */
+export type SliceMatch = {
+    kind: "value" | "type";
+    value: Record<string, unknown>;
+};
+
 export interface FieldSlice {
     min?: number;
     max?: number;
-    match?: Record<string, unknown>;
+    match?: SliceMatch;
     required?: string[];
     excluded?: string[];
     elements?: string[];
diff --git a/src/typeschema/utils.ts b/src/typeschema/utils.ts
index f6b7b0f2..2b5ee900 100644
--- a/src/typeschema/utils.ts
+++ b/src/typeschema/utils.ts
@@ -739,7 +739,7 @@ export const mkTypeSchemaIndex = (
     /** Compute the derived facts for one slice; returns a copy — the source
      *  profile schemas stay untouched. */
     const enrichSlice = (slice: FieldSlice, ctx: SliceEnrichmentContext): FieldSlice => {
-        const matchKeys = new Set(Object.keys(slice.match ?? {}));
+        const matchKeys = new Set(Object.keys(slice.match?.value ?? {}));
         const required = slice.required ?? [];
         const effectiveRequired = required.filter((n) => !matchKeys.has(n) && !ctx.choiceBaseNames.has(n));
         // Stub eligibility keeps choice-base names: a slice requiring its
@@ -749,7 +749,7 @@ export const mkTypeSchemaIndex = (
             !ctx.typeDiscriminated && (slice.min ?? 0) >= 1 && matchKeys.size > 0 && requiredBeyondMatch.length === 0;
         const cc =
             ctx.fieldType && slice.elements ? constrainedChoice(ctx.pkgName, ctx.fieldType, slice.elements) : undefined;
-        const resourceType = ctx.typeDiscriminated ? extractResourceTypeFromMatch(slice.match ?? {}) : undefined;
+        const resourceType = ctx.typeDiscriminated ? extractResourceTypeFromMatch(slice.match?.value ?? {}) : undefined;
         return {
             ...slice,
             ...(effectiveRequired.length > 0 ? { effectiveRequired } : {}),
diff --git a/test/api/write-generator/__snapshots__/introspection.test.ts.snap b/test/api/write-generator/__snapshots__/introspection.test.ts.snap
index db0dc027..4c7cff1b 100644
--- a/test/api/write-generator/__snapshots__/introspection.test.ts.snap
+++ b/test/api/write-generator/__snapshots__/introspection.test.ts.snap
@@ -3143,12 +3143,15 @@ exports[`IntrospectionWriter - flat profile output Check bodyweight flat profile
           "min": 1,
           "max": 1,
           "match": {
-            "coding": [
-              {
-                "code": "vital-signs",
-                "system": "http://terminology.hl7.org/CodeSystem/observation-category"
-              }
-            ]
+            "kind": "value",
+            "value": {
+              "coding": [
+                {
+                  "code": "vital-signs",
+                  "system": "http://terminology.hl7.org/CodeSystem/observation-category"
+                }
+              ]
+            }
           },
           "required": [
             "coding"

From 78ffce75599de603e603fded633f5faecaf1ad19 Mon Sep 17 00:00:00 2001
From: Aleksandr Penskoi <alexandr.penskoi@health-samurai.io>
Date: Fri, 24 Jul 2026 18:21:08 +0400
Subject: [PATCH 7/9] feat(typeschema): merge inherited slices when a profile
 re-slices a field

flatProfile previously replaced the whole inherited FieldSlicing when a
child profile restated slicing on the same field. Now the child refines it:
its header and same-name slices win, inherited slices survive.
---
 src/typeschema/utils.ts                       | 19 ++++-
 test/unit/typeschema/slice-enrichment.test.ts | 77 +++++++++++++++++++
 2 files changed, 94 insertions(+), 2 deletions(-)

diff --git a/src/typeschema/utils.ts b/src/typeschema/utils.ts
index 2b5ee900..1583848c 100644
--- a/src/typeschema/utils.ts
+++ b/src/typeschema/utils.ts
@@ -637,8 +637,23 @@ export const mkTypeSchemaIndex = (
         const mergedSlicing = {} as Record<string, FieldSlicing>;
         for (const anySchema of constraintSchemas.slice().reverse()) {
             const schema = anySchema as SpecializationTypeSchema;
-            // Leaf-most slicing wins per field, mirroring the field merge below.
-            if (schema.slicing) Object.assign(mergedSlicing, schema.slicing);
+            // Slice-level merge: a re-slicing profile refines the inherited slice
+            // set — its header and same-name slices win, inherited slices survive.
+            if (schema.slicing) {
+                for (const [fieldName, fieldSlicing] of Object.entries(schema.slicing)) {
+                    const base = mergedSlicing[fieldName];
+                    if (!base) {
+                        mergedSlicing[fieldName] = fieldSlicing;
+                        continue;
+                    }
+                    const slices = { ...base.slices, ...fieldSlicing.slices };
+                    mergedSlicing[fieldName] = {
+                        ...base,
+                        ...fieldSlicing,
+                        ...(Object.keys(slices).length > 0 ? { slices } : {}),
+                    };
+                }
+            }
             if (!schema.fields) continue;
 
             for (const [fieldName, fieldConstraints] of Object.entries(schema.fields)) {
diff --git a/test/unit/typeschema/slice-enrichment.test.ts b/test/unit/typeschema/slice-enrichment.test.ts
index 93b9d8f1..d3bc0ece 100644
--- a/test/unit/typeschema/slice-enrichment.test.ts
+++ b/test/unit/typeschema/slice-enrichment.test.ts
@@ -123,3 +123,80 @@ describe("slice enrichment on profile snapshots", async () => {
         expect(slice?.autoStub).toBeUndefined();
     });
 });
+
+describe("slicing merge across the profile chain", async () => {
+    const r4 = await mkR4Register();
+    const logger = mkErrorLogger();
+
+    registerFs(r4, {
+        url: "http://example.org/StructureDefinition/SlicedParent",
+        name: "SlicedParent",
+        base: "http://hl7.org/fhir/StructureDefinition/Observation",
+        derivation: "constraint",
+        kind: "resource",
+        elements: {
+            category: {
+                type: "CodeableConcept",
+                array: true,
+                slicing: {
+                    discriminator: [{ type: "pattern", path: "$this" }],
+                    rules: "open",
+                    slices: {
+                        FromParent: { min: 1, max: 1, match: { coding: [{ code: "parent" }] } },
+                    },
+                },
+            },
+        },
+    });
+
+    registerFs(r4, {
+        url: "http://example.org/StructureDefinition/SlicedChild",
+        name: "SlicedChild",
+        base: "http://example.org/StructureDefinition/SlicedParent",
+        derivation: "constraint",
+        kind: "resource",
+        elements: {
+            category: {
+                type: "CodeableConcept",
+                array: true,
+                slicing: {
+                    discriminator: [{ type: "pattern", path: "$this" }],
+                    rules: "open",
+                    slices: {
+                        FromChild: { max: 1, match: { coding: [{ code: "child" }] } },
+                        FromParent: { min: 0, max: 1, match: { coding: [{ code: "parent-refined" }] } },
+                    },
+                },
+            },
+        },
+    });
+
+    const schemas: TypeSchema[] = [];
+    for (const [pkg, url] of [
+        [myPkg, "http://example.org/StructureDefinition/SlicedParent"],
+        [myPkg, "http://example.org/StructureDefinition/SlicedChild"],
+        [r4Package, "http://hl7.org/fhir/StructureDefinition/Observation"],
+        [r4Package, "http://hl7.org/fhir/StructureDefinition/DomainResource"],
+        [r4Package, "http://hl7.org/fhir/StructureDefinition/Resource"],
+    ] as const) {
+        schemas.push(...(await resolveTs(r4, pkg, url as CanonicalUrl, logger)));
+    }
+    const tsIndex = mkTypeSchemaIndex(schemas, { register: r4, logger });
+
+    const childSnapshot = () => {
+        const snap = tsIndex.collectSnapshotProfiles().find((s) => s.identifier.name === "SlicedChild");
+        if (!snap) throw new Error("No snapshot for SlicedChild");
+        return snap;
+    };
+
+    it("re-slicing keeps inherited slices and adds new ones", () => {
+        const slices = childSnapshot().slicing?.category?.slices ?? {};
+        expect(Object.keys(slices).sort()).toEqual(["FromChild", "FromParent"]);
+    });
+
+    it("same-name slices from the leaf win", () => {
+        const fromParent = childSnapshot().slicing?.category?.slices?.FromParent;
+        expect(fromParent?.match?.value).toEqual({ coding: [{ code: "parent-refined" }] });
+        expect(fromParent?.min).toBe(0);
+    });
+});

From 4f0368fa9a36f8b4bf7b8bee9e40ed259fa9eb3c Mon Sep 17 00:00:00 2001
From: Aleksandr Penskoi <alexandr.penskoi@health-samurai.io>
Date: Fri, 24 Jul 2026 18:34:23 +0400
Subject: [PATCH 8/9] feat(typeschema): fully populate extension-style slice
 entries; make extension-slice ownership explicit

Extension-style slices carry their discriminator value as schema.url and
their cardinality on the slice schema (fhirschema convention); buildSlicing
now recovers both, so the slicing map has no degenerate entries. Writers
replace the accidental skip (missing match) with an explicit rule: on
resource-based profiles, extension/modifierExtension slices are owned by the
ProfileExtension mechanism; on Extension-based profiles the slice machinery
keeps generating the sub-extension slice API as before. Generated output is
unchanged.
---
 .../python/profile-factory.ts                 |  6 ++++-
 .../writer-generator/python/profile-slices.ts |  2 ++
 .../python/profile-validation.ts              |  5 +++-
 .../typescript/profile-slices.ts              |  3 +++
 .../typescript/profile-validation.ts          |  5 +++-
 .../writer-generator/typescript/profile.ts    |  7 ++++--
 src/api/writer-generator/utils.ts             |  5 ++++
 src/typeschema/core/field-builder.ts          | 25 +++++++++++++++----
 .../kbv-condition-diagnosis.test.ts.snap      | 14 +++++++++++
 9 files changed, 62 insertions(+), 10 deletions(-)

diff --git a/src/api/writer-generator/python/profile-factory.ts b/src/api/writer-generator/python/profile-factory.ts
index 6cbd9609..92218470 100644
--- a/src/api/writer-generator/python/profile-factory.ts
+++ b/src/api/writer-generator/python/profile-factory.ts
@@ -1,3 +1,4 @@
+import { isExtensionOwnedField } from "@root/api/writer-generator/utils";
 import {
     type ChoiceFieldInstance,
     type Field,
@@ -174,7 +175,10 @@ export const collectProfileFactoryInfo = (
         }
 
         if (isNotChoiceDeclarationField(field)) {
-            const sliceNames = collectRequiredSliceNames(field, flatProfile.slicing?.[name]);
+            const sliceNames =
+                isExtensionOwnedField(name) && flatProfile.base.name !== "Extension"
+                    ? undefined
+                    : collectRequiredSliceNames(field, flatProfile.slicing?.[name]);
             // Extension profiles populate `extension` via sub-extension slice
             // setters — keep it optional in create() even when no slice is
             // auto-stubbable (mirrors the optional `extension` in the TS Raw type).
diff --git a/src/api/writer-generator/python/profile-slices.ts b/src/api/writer-generator/python/profile-slices.ts
index 207992ef..ccd16742 100644
--- a/src/api/writer-generator/python/profile-slices.ts
+++ b/src/api/writer-generator/python/profile-slices.ts
@@ -1,3 +1,4 @@
+import { isExtensionOwnedField } from "@root/api/writer-generator/utils";
 import {
     type ConstrainedChoiceInfo,
     type FieldSlicing,
@@ -92,6 +93,7 @@ export const normalizeMatchForPython = (
 
 export const collectSliceDefs = (tsIndex: TypeSchemaIndex, flatProfile: SnapshotProfileTypeSchema): SliceDef[] => {
     return Object.entries(flatProfile.slicing ?? {}).flatMap(([fieldName, fieldSlicing]) => {
+        if (isExtensionOwnedField(fieldName) && flatProfile.base.name !== "Extension") return [];
         const field = flatProfile.fields[fieldName];
         if (!isNotChoiceDeclarationField(field) || !fieldSlicing.slices || !field.type) return [];
         const baseSchema = tsIndex.resolveType(field.type);
diff --git a/src/api/writer-generator/python/profile-validation.ts b/src/api/writer-generator/python/profile-validation.ts
index 5ff24961..5719210a 100644
--- a/src/api/writer-generator/python/profile-validation.ts
+++ b/src/api/writer-generator/python/profile-validation.ts
@@ -1,3 +1,4 @@
+import { isExtensionOwnedField } from "@root/api/writer-generator/utils";
 import {
     type ChoiceFieldInstance,
     type FieldSlicing,
@@ -61,7 +62,9 @@ export const collectValidateBody = (
         }
         collectRegularFieldValidation(
             field,
-            flatProfile.slicing?.[name],
+            isExtensionOwnedField(name) && flatProfile.base.name !== "Extension"
+                ? undefined
+                : flatProfile.slicing?.[name],
             pyName,
             helpers,
             errorLines,
diff --git a/src/api/writer-generator/typescript/profile-slices.ts b/src/api/writer-generator/typescript/profile-slices.ts
index 758f825c..50ca239e 100644
--- a/src/api/writer-generator/typescript/profile-slices.ts
+++ b/src/api/writer-generator/typescript/profile-slices.ts
@@ -1,3 +1,4 @@
+import { isExtensionOwnedField } from "@root/api/writer-generator/utils";
 import {
     type ConstrainedChoiceInfo,
     type FieldSlicing,
@@ -26,6 +27,7 @@ export const collectTypesFromSlices = (
     addType: (typeId: TypeIdentifier) => void,
 ) => {
     for (const [fieldName, fieldSlicing] of Object.entries(snapshot.slicing ?? {})) {
+        if (isExtensionOwnedField(fieldName) && snapshot.base.name !== "Extension") continue;
         const field = snapshot.fields[fieldName];
         if (!isNotChoiceDeclarationField(field) || !fieldSlicing.slices || !field.type) continue;
         for (const slice of Object.values(fieldSlicing.slices)) {
@@ -84,6 +86,7 @@ export type SliceDef = {
 
 export const collectSliceDefs = (_tsIndex: TypeSchemaIndex, snapshot: SnapshotProfileTypeSchema): SliceDef[] =>
     Object.entries(snapshot.slicing ?? {}).flatMap(([fieldName, fieldSlicing]) => {
+        if (isExtensionOwnedField(fieldName) && snapshot.base.name !== "Extension") return [];
         const field = snapshot.fields[fieldName];
         if (!isNotChoiceDeclarationField(field) || !fieldSlicing.slices || !field.type) return [];
         const baseType = tsTypeFromIdentifier(field.type);
diff --git a/src/api/writer-generator/typescript/profile-validation.ts b/src/api/writer-generator/typescript/profile-validation.ts
index b10090e5..2ecb4267 100644
--- a/src/api/writer-generator/typescript/profile-validation.ts
+++ b/src/api/writer-generator/typescript/profile-validation.ts
@@ -1,3 +1,4 @@
+import { isExtensionOwnedField } from "@root/api/writer-generator/utils";
 import {
     type ChoiceFieldInstance,
     type FieldSlicing,
@@ -109,7 +110,9 @@ export const generateValidateMethod = (
                 tsIndex.findLastSpecializationByIdentifier,
                 canonicalUrlExpr,
                 tsIndex,
-                snapshot.slicing?.[name],
+                isExtensionOwnedField(name) && snapshot.base.name !== "Extension"
+                    ? undefined
+                    : snapshot.slicing?.[name],
             );
         }
 
diff --git a/src/api/writer-generator/typescript/profile.ts b/src/api/writer-generator/typescript/profile.ts
index d3d49dba..ab66ded8 100644
--- a/src/api/writer-generator/typescript/profile.ts
+++ b/src/api/writer-generator/typescript/profile.ts
@@ -1,4 +1,4 @@
-import { pascalCase, uppercaseFirstLetter } from "@root/api/writer-generator/utils";
+import { isExtensionOwnedField, pascalCase, uppercaseFirstLetter } from "@root/api/writer-generator/utils";
 import {
     type CanonicalUrl,
     isChoiceDeclarationField,
@@ -166,7 +166,10 @@ export const collectProfileFactoryInfo = (
         }
 
         if (isNotChoiceDeclarationField(field)) {
-            const sliceNames = collectRequiredSliceNames(field, snapshot.slicing?.[name]);
+            const sliceNames =
+                isExtensionOwnedField(name) && snapshot.base.name !== "Extension"
+                    ? undefined
+                    : collectRequiredSliceNames(field, snapshot.slicing?.[name]);
             if (sliceNames) {
                 if (field.type) {
                     const tsType = fieldTsType(field, resolveRef, isFamilyType);
diff --git a/src/api/writer-generator/utils.ts b/src/api/writer-generator/utils.ts
index 67b7e46c..23174bb6 100644
--- a/src/api/writer-generator/utils.ts
+++ b/src/api/writer-generator/utils.ts
@@ -63,3 +63,8 @@ export function deepEqual<T>(obj1: T, obj2: T): boolean {
 
     return keys1.every((key) => keys2.includes(key) && deepEqual(obj1[key], obj2[key]));
 }
+
+/** Slices on `extension`/`modifierExtension` are owned by the ProfileExtension
+ *  mechanism — the generic slice machinery must not double-generate for them. */
+export const isExtensionOwnedField = (fieldName: string): boolean =>
+    fieldName === "extension" || fieldName === "modifierExtension";
diff --git a/src/typeschema/core/field-builder.ts b/src/typeschema/core/field-builder.ts
index c3b91736..84d4804c 100644
--- a/src/typeschema/core/field-builder.ts
+++ b/src/typeschema/core/field-builder.ts
@@ -291,21 +291,36 @@ const computeMatchFromSchema = (
     return result;
 };
 
+/** Extension-style slices carry their discriminator value as `schema.url`
+ *  (fhirschema convention) rather than under `elements` — recover the match
+ *  when the slicing discriminates on `url`. */
+const extensionUrlMatch = (
+    discriminators: FHIRSchemaDiscriminator[],
+    schema: FHIRSchemaElement | undefined,
+): Record<string, unknown> | undefined => {
+    if (!schema || typeof schema.url !== "string") return undefined;
+    const byUrl = discriminators.some((d) => (d.type === "value" || d.type === "pattern") && d.path === "url");
+    return byUrl ? { url: schema.url } : undefined;
+};
+
 export const buildSlicing = (fieldName: string, element: FHIRSchemaElement): FieldSlicing | undefined => {
     const slicing = element.slicing;
     if (!slicing) return undefined;
 
-    const matchKind: SliceMatch["kind"] = slicing.discriminator?.some((d) => d.type === "type") ? "type" : "value";
+    const discriminators = slicing.discriminator ?? [];
+    const matchKind: SliceMatch["kind"] = discriminators.some((d) => d.type === "type") ? "type" : "value";
     const slices: Record<string, FieldSlice> = {};
     for (const [name, slice] of Object.entries(slicing.slices ?? {})) {
         if (!slice) continue;
         const { required, excluded, elements } = slice.schema ? extractSliceFieldNames(slice.schema) : {};
-        const matchValue = isEmptyMatch(slice.match)
-            ? computeMatchFromSchema(slicing.discriminator ?? [], slice.schema)
+        const computed = isEmptyMatch(slice.match)
+            ? computeMatchFromSchema(discriminators, slice.schema)
             : (slice.match as Record<string, unknown> | undefined);
+        const matchValue = isEmptyMatch(computed) ? extensionUrlMatch(discriminators, slice.schema) : computed;
         slices[name] = {
-            min: slice.min,
-            max: slice.max,
+            // Extension-style slices keep their cardinality on the slice schema.
+            min: slice.min ?? slice.schema?.min,
+            max: slice.max ?? slice.schema?.max,
             match:
                 matchValue && Object.keys(matchValue).length > 0 ? { kind: matchKind, value: matchValue } : undefined,
             required,
diff --git a/test/api/write-generator/__snapshots__/kbv-condition-diagnosis.test.ts.snap b/test/api/write-generator/__snapshots__/kbv-condition-diagnosis.test.ts.snap
index 3c337369..b97676bf 100644
--- a/test/api/write-generator/__snapshots__/kbv-condition-diagnosis.test.ts.snap
+++ b/test/api/write-generator/__snapshots__/kbv-condition-diagnosis.test.ts.snap
@@ -2236,7 +2236,14 @@ exports[`KBV Condition Diagnosis generation (kbv.basis@1.9.0) TypeSchema: KBV_PR
       "rules": "open",
       "slices": {
         "Feststellungsdatum": {
+          "min": 0,
           "max": 1,
+          "match": {
+            "kind": "value",
+            "value": {
+              "url": "http://hl7.org/fhir/StructureDefinition/condition-assertedDate"
+            }
+          },
           "nameCandidates": {
             "candidates": [
               "Feststellungsdatum",
@@ -3051,7 +3058,14 @@ exports[`KBV Condition Diagnosis generation (kbv.basis@1.9.0) TypeSchema: KBV_PR
       "rules": "open",
       "slices": {
         "Feststellungsdatum": {
+          "min": 0,
           "max": 1,
+          "match": {
+            "kind": "value",
+            "value": {
+              "url": "http://hl7.org/fhir/StructureDefinition/condition-assertedDate"
+            }
+          },
           "nameCandidates": {
             "candidates": [
               "Feststellungsdatum",

From 4f92d18992e60a50f9baa89b667d12eac35b7d26 Mon Sep 17 00:00:00 2001
From: Aleksandr Penskoi <alexandr.penskoi@health-samurai.io>
Date: Mon, 27 Jul 2026 10:24:39 +0400
Subject: [PATCH 9/9] docs: document slicing model and FieldReference in the
 TypeSchema JSON schema
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Adds field-slicing/field-slice/slice-match/slice-discriminator definitions —
including the snapshot-time derived facts (effectiveRequired,
constrainedChoice, autoStub, resourceType) — attaches the schema-level
'slicing' map next to 'fields', and updates 'reference' to the
{ resource, profiles } shape.
---
 docs/type-schema.schema.json | 443 ++++++++++++++++++++++++++++++-----
 1 file changed, 381 insertions(+), 62 deletions(-)

diff --git a/docs/type-schema.schema.json b/docs/type-schema.schema.json
index 4dd7433b..7d3e0685 100644
--- a/docs/type-schema.schema.json
+++ b/docs/type-schema.schema.json
@@ -9,13 +9,27 @@
 		"type-schema-identifier": {
 			"type": "object",
 			"oneOf": [
-				{ "$ref": "#/definitions/with-primitive-type-kind" },
-				{ "$ref": "#/definitions/with-valueset-kind" },
-				{ "$ref": "#/definitions/with-complex-type-kind" },
-				{ "$ref": "#/definitions/with-resource-kind" },
-				{ "$ref": "#/definitions/with-nested-kind" },
-				{ "$ref": "#/definitions/with-logical-kind" },
-				{ "$ref": "#/definitions/with-binding-kind" }
+				{
+					"$ref": "#/definitions/with-primitive-type-kind"
+				},
+				{
+					"$ref": "#/definitions/with-valueset-kind"
+				},
+				{
+					"$ref": "#/definitions/with-complex-type-kind"
+				},
+				{
+					"$ref": "#/definitions/with-resource-kind"
+				},
+				{
+					"$ref": "#/definitions/with-nested-kind"
+				},
+				{
+					"$ref": "#/definitions/with-logical-kind"
+				},
+				{
+					"$ref": "#/definitions/with-binding-kind"
+				}
 			],
 			"properties": {
 				"kind": {
@@ -39,56 +53,76 @@
 					"description": "A canonical URL identifying this resource uniquely in the FHIR ecosystem"
 				}
 			},
-			"required": ["kind", "package", "version", "name", "url"],
+			"required": [
+				"kind",
+				"package",
+				"version",
+				"name",
+				"url"
+			],
 			"additionalProperties": false
 		},
 		"with-primitive-type-kind": {
 			"type": "object",
 			"description": "Constraint helper to ensure the kind is primitive-type",
 			"properties": {
-				"kind": { "const": "primitive-type" }
+				"kind": {
+					"const": "primitive-type"
+				}
 			}
 		},
 		"with-valueset-kind": {
 			"type": "object",
 			"description": "Constraint helper to ensure the kind is value-set",
 			"properties": {
-				"kind": { "const": "value-set" }
+				"kind": {
+					"const": "value-set"
+				}
 			}
 		},
 		"with-binding-kind": {
 			"type": "object",
 			"description": "Constraint helper to ensure the kind is value-set",
 			"properties": {
-				"kind": { "const": "binding" }
+				"kind": {
+					"const": "binding"
+				}
 			}
 		},
 		"with-complex-type-kind": {
 			"type": "object",
 			"description": "Constraint helper to ensure the kind is complex-type",
 			"properties": {
-				"kind": { "const": "complex-type" }
+				"kind": {
+					"const": "complex-type"
+				}
 			}
 		},
 		"with-resource-kind": {
 			"type": "object",
 			"description": "Constraint helper to ensure the kind is resource",
 			"properties": {
-				"kind": { "const": "resource" }
+				"kind": {
+					"const": "resource"
+				}
 			}
 		},
 		"with-nested-kind": {
 			"type": "object",
 			"description": "Constraint helper to ensure the kind is nested",
 			"properties": {
-				"kind": { "const": "nested" }
+				"kind": {
+					"const": "nested"
+				}
 			}
 		},
 		"with-logical-kind": {
 			"type": "object",
 			"description": "Constraint helper to ensure the kind is logical",
 			"properties": {
-				"kind": { "const": "logical" }
+				"kind": {
+					"const": "logical"
+				}
 			}
 		},
 		"field.regular": {
@@ -101,11 +135,28 @@
 					"description": "The data type of this field"
 				},
 				"reference": {
-					"type": "array",
-					"description": "Reference to other types that this field can point to",
-					"items": {
-						"$ref": "#/definitions/type-schema-identifier"
-					}
+					"type": "object",
+					"description": "Reference targets, split into two independent facts: base resource types a reference literal may point at, and profile conformance expectations from targetProfile",
+					"properties": {
+						"resource": {
+							"type": "array",
+							"description": "Base resource types a reference value may point at; profile targets are resolved to their base specialization and deduplicated",
+							"items": {
+								"$ref": "#/definitions/type-schema-identifier"
+							}
+						},
+						"profiles": {
+							"type": "array",
+							"description": "Profile conformance expectations from targetProfile — reference values in instances always use base resource types",
+							"items": {
+								"$ref": "#/definitions/type-schema-identifier"
+							}
+						}
+					},
+					"required": [
+						"resource"
+					],
+					"additionalProperties": false
 				},
 				"required": {
 					"type": "boolean",
@@ -124,13 +175,19 @@
 				},
 				"binding": {
 					"allOf": [
-						{ "$ref": "#/definitions/type-schema-identifier" },
-						{ "$ref": "#/definitions/with-binding-kind" }
+						{
+							"$ref": "#/definitions/type-schema-identifier"
+						},
+						{
+							"$ref": "#/definitions/with-binding-kind"
+						}
 					]
 				},
 				"enum": {
 					"type": "array",
-					"items": { "type": "string" },
+					"items": {
+						"type": "string"
+					},
 					"description": "For code fields, the set of valid values when bound to a required value set"
 				},
 				"min": {
@@ -142,10 +199,11 @@
 					"description": "Maximum limit of items for an array"
 				}
 			},
-			"required": ["type"],
+			"required": [
+				"type"
+			],
 			"additionalProperties": false
 		},
-
 		"field.polymorphic-declaration": {
 			"title": "Polymorphic value[x] field declaration",
 			"description": "The base declaration for a FHIR choice type (e.g., value[x])",
@@ -153,7 +211,9 @@
 			"properties": {
 				"choices": {
 					"type": "array",
-					"items": { "type": "string" },
+					"items": {
+						"type": "string"
+					},
 					"description": "The names of all concrete type options for this choice field"
 				},
 				"required": {
@@ -180,10 +240,11 @@
 					"description": "Maximum limit of items for an array"
 				}
 			},
-			"required": ["choices"],
+			"required": [
+				"choices"
+			],
 			"additionalProperties": false
 		},
-
 		"field.polymorphic-instance": {
 			"title": "Polymorphic value[x] field instance",
 			"description": "A specific type option for a FHIR choice type (e.g., valueString, valueInteger)",
@@ -221,14 +282,20 @@
 				},
 				"binding": {
 					"allOf": [
-						{ "$ref": "#/definitions/type-schema-identifier" },
-						{ "$ref": "#/definitions/with-binding-kind" }
+						{
+							"$ref": "#/definitions/type-schema-identifier"
+						},
+						{
+							"$ref": "#/definitions/with-binding-kind"
+						}
 					],
 					"description": "For coded choices, information about the value set binding"
 				},
 				"enum": {
 					"type": "array",
-					"items": { "type": "string" },
+					"items": {
+						"type": "string"
+					},
 					"description": "For code fields, the set of valid values when bound to a required value set"
 				},
 				"min": {
@@ -240,7 +307,10 @@
 					"description": "Maximum limit of items for an array"
 				}
 			},
-			"required": ["type", "choiceOf"],
+			"required": [
+				"type",
+				"choiceOf"
+			],
 			"additionalProperties": false
 		},
 		"dependencies": {
@@ -249,9 +319,193 @@
 			"items": {
 				"$ref": "#/definitions/type-schema-identifier"
 			}
+		},
+		"slice-discriminator": {
+			"title": "Slice discriminator",
+			"description": "How slice membership is decided (ElementDefinition.slicing.discriminator)",
+			"type": "object",
+			"properties": {
+				"type": {
+					"type": "string",
+					"enum": [
+						"value",
+						"exists",
+						"pattern",
+						"type",
+						"profile",
+						"position"
+					]
+				},
+				"path": {
+					"type": "string"
+				}
+			},
+			"required": [
+				"type",
+				"path"
+			],
+			"additionalProperties": false
+		},
+		"slice-match": {
+			"title": "Slice match",
+			"description": "How a slice is recognized in instance data. 'value' holds the discriminator values keyed by element name and is used verbatim for runtime matching; 'kind' says whether they come from fixed/pattern discriminator values ('value') or a resource-type discriminator ('type')",
+			"type": "object",
+			"properties": {
+				"kind": {
+					"type": "string",
+					"enum": [
+						"value",
+						"type"
+					]
+				},
+				"value": {
+					"type": "object"
+				}
+			},
+			"required": [
+				"kind",
+				"value"
+			],
+			"additionalProperties": false
+		},
+		"field-slice": {
+			"title": "Field slice",
+			"description": "One slice of a sliced element. Besides the source facts, profile snapshots carry derived facts computed at snapshot build so generators share one implementation",
+			"type": "object",
+			"properties": {
+				"min": {
+					"type": "number",
+					"description": "Minimum number of elements matching this slice"
+				},
+				"max": {
+					"type": "number",
+					"description": "Maximum number of elements matching this slice (0 = unbounded)"
+				},
+				"match": {
+					"$ref": "#/definitions/slice-match"
+				},
+				"required": {
+					"type": "array",
+					"items": {
+						"type": "string"
+					},
+					"description": "Required sub-element names inside a matched element"
+				},
+				"excluded": {
+					"type": "array",
+					"items": {
+						"type": "string"
+					},
+					"description": "Prohibited sub-element names inside a matched element"
+				},
+				"elements": {
+					"type": "array",
+					"items": {
+						"type": "string"
+					},
+					"description": "Sub-element names the slice constrains"
+				},
+				"nameCandidates": {
+					"type": "object",
+					"description": "Collision-free name candidates for generated accessors",
+					"properties": {
+						"candidates": {
+							"type": "array",
+							"items": {
+								"type": "string"
+							}
+						},
+						"recommended": {
+							"type": "string"
+						}
+					},
+					"required": [
+						"candidates",
+						"recommended"
+					],
+					"additionalProperties": false
+				},
+				"effectiveRequired": {
+					"type": "array",
+					"items": {
+						"type": "string"
+					},
+					"description": "Derived (profile snapshots): 'required' minus match keys and choice-declaration base names — the sub-elements validators must check"
+				},
+				"constrainedChoice": {
+					"type": "object",
+					"description": "Derived (profile snapshots): the single choice variant this slice constrains (e.g. BP component value[x] narrowed to valueQuantity)",
+					"properties": {
+						"choiceBase": {
+							"type": "string"
+						},
+						"variant": {
+							"type": "string"
+						},
+						"variantType": {
+							"$ref": "#/definitions/type-schema-identifier"
+						},
+						"allChoiceNames": {
+							"type": "array",
+							"items": {
+								"type": "string"
+							}
+						}
+					},
+					"required": [
+						"choiceBase",
+						"variant",
+						"variantType",
+						"allChoiceNames"
+					],
+					"additionalProperties": false
+				},
+				"autoStub": {
+					"type": "boolean",
+					"description": "Derived (profile snapshots): the slice can be auto-populated with just the discriminator match values"
+				},
+				"resourceType": {
+					"type": "string",
+					"description": "Derived (profile snapshots): matched resource type for type-discriminated slices (e.g. Bundle entry -> Patient)"
+				}
+			},
+			"required": [
+				"nameCandidates"
+			],
+			"additionalProperties": false
+		},
+		"field-slicing": {
+			"title": "Field slicing",
+			"description": "Slicing definition for one sliced element, keyed by field name in the schema-level 'slicing' map — kept apart from 'fields': fields describe the data shape, slicing is an independent constraint layer",
+			"type": "object",
+			"properties": {
+				"discriminator": {
+					"type": "array",
+					"items": {
+						"$ref": "#/definitions/slice-discriminator"
+					}
+				},
+				"rules": {
+					"type": "string",
+					"enum": [
+						"open",
+						"closed",
+						"openAtEnd"
+					]
+				},
+				"ordered": {
+					"type": "boolean"
+				},
+				"slices": {
+					"type": "object",
+					"additionalProperties": {
+						"$ref": "#/definitions/field-slice"
+					}
+				}
+			},
+			"additionalProperties": false
 		}
 	},
-
 	"oneOf": [
 		{
 			"title": "Type Schema for Primitive Type",
@@ -260,8 +514,12 @@
 			"properties": {
 				"identifier": {
 					"allOf": [
-						{ "$ref": "#/definitions/type-schema-identifier" },
-						{ "$ref": "#/definitions/with-primitive-type-kind" }
+						{
+							"$ref": "#/definitions/type-schema-identifier"
+						},
+						{
+							"$ref": "#/definitions/with-primitive-type-kind"
+						}
 					],
 					"description": "The unique identifier for this primitive type"
 				},
@@ -278,10 +536,12 @@
 					"description": "Other types that this primitive type depends on"
 				}
 			},
-			"required": ["identifier", "base"],
+			"required": [
+				"identifier",
+				"base"
+			],
 			"additionalProperties": false
 		},
-
 		{
 			"title": "Type Schema for Resource, Complex Type, Logical",
 			"description": "Schema for FHIR resources, complex types, and logical types",
@@ -289,12 +549,20 @@
 			"properties": {
 				"identifier": {
 					"allOf": [
-						{ "$ref": "#/definitions/type-schema-identifier" },
+						{
+							"$ref": "#/definitions/type-schema-identifier"
+						},
 						{
 							"oneOf": [
-								{ "$ref": "#/definitions/with-resource-kind" },
-								{ "$ref": "#/definitions/with-complex-type-kind" },
-								{ "$ref": "#/definitions/with-logical-kind" }
+								{
+									"$ref": "#/definitions/with-resource-kind"
+								},
+								{
+									"$ref": "#/definitions/with-complex-type-kind"
+								},
+								{
+									"$ref": "#/definitions/with-logical-kind"
+								}
 							]
 						}
 					],
@@ -313,12 +581,25 @@
 					"description": "The fields contained in this resource or type",
 					"additionalProperties": {
 						"anyOf": [
-							{ "$ref": "#/definitions/field.regular" },
-							{ "$ref": "#/definitions/field.polymorphic-declaration" },
-							{ "$ref": "#/definitions/field.polymorphic-instance" }
+							{
+								"$ref": "#/definitions/field.regular"
+							},
+							{
+								"$ref": "#/definitions/field.polymorphic-declaration"
+							},
+							{
+								"$ref": "#/definitions/field.polymorphic-instance"
+							}
 						]
 					}
 				},
+				"slicing": {
+					"type": "object",
+					"description": "Slicing definitions keyed by field name, kept apart from 'fields'",
+					"additionalProperties": {
+						"$ref": "#/definitions/field-slicing"
+					}
+				},
 				"nested": {
 					"type": "array",
 					"description": "BackboneElement types nested within this resource or type",
@@ -327,8 +608,12 @@
 						"properties": {
 							"identifier": {
 								"allOf": [
-									{ "$ref": "#/definitions/type-schema-identifier" },
-									{ "$ref": "#/definitions/with-nested-kind" }
+									{
+										"$ref": "#/definitions/type-schema-identifier"
+									},
+									{
+										"$ref": "#/definitions/with-nested-kind"
+									}
 								],
 								"description": "The unique identifier for this nested type"
 							},
@@ -341,14 +626,30 @@
 								"description": "The fields contained in this nested type",
 								"additionalProperties": {
 									"anyOf": [
-										{ "$ref": "#/definitions/field.regular" },
-										{ "$ref": "#/definitions/field.polymorphic-declaration" },
-										{ "$ref": "#/definitions/field.polymorphic-instance" }
+										{
+											"$ref": "#/definitions/field.regular"
+										},
+										{
+											"$ref": "#/definitions/field.polymorphic-declaration"
+										},
+										{
+											"$ref": "#/definitions/field.polymorphic-instance"
+										}
 									]
 								}
+							},
+							"slicing": {
+								"type": "object",
+								"description": "Slicing definitions keyed by field name, kept apart from 'fields'",
+								"additionalProperties": {
+									"$ref": "#/definitions/field-slicing"
+								}
 							}
 						},
-						"required": ["identifier", "base"],
+						"required": [
+							"identifier",
+							"base"
+						],
 						"additionalProperties": false
 					}
 				},
@@ -360,10 +661,11 @@
 					}
 				}
 			},
-			"required": ["identifier"],
+			"required": [
+				"identifier"
+			],
 			"additionalProperties": false
 		},
-
 		{
 			"title": "Type Schema for ValueSet",
 			"description": "Schema for FHIR value sets that define terminology bindings",
@@ -371,8 +673,12 @@
 			"properties": {
 				"identifier": {
 					"allOf": [
-						{ "$ref": "#/definitions/type-schema-identifier" },
-						{ "$ref": "#/definitions/with-valueset-kind" }
+						{
+							"$ref": "#/definitions/type-schema-identifier"
+						},
+						{
+							"$ref": "#/definitions/with-valueset-kind"
+						}
 					],
 					"description": "The unique identifier for this value set"
 				},
@@ -399,7 +705,9 @@
 								"description": "The code system URL that defines this code"
 							}
 						},
-						"required": ["code"],
+						"required": [
+							"code"
+						],
 						"additionalProperties": false
 					}
 				},
@@ -408,18 +716,23 @@
 					"description": "Complex value set composition rules when the value set is defined as a composition of other value sets"
 				}
 			},
-			"required": ["identifier"],
+			"required": [
+				"identifier"
+			],
 			"additionalProperties": false
 		},
-
 		{
 			"title": "Type Schema for Binding",
 			"type": "object",
 			"properties": {
 				"identifier": {
 					"allOf": [
-						{ "$ref": "#/definitions/type-schema-identifier" },
-						{ "$ref": "#/definitions/with-binding-kind" }
+						{
+							"$ref": "#/definitions/type-schema-identifier"
+						},
+						{
+							"$ref": "#/definitions/with-binding-kind"
+						}
 					],
 					"description": "The unique identifier for this value set"
 				},
@@ -443,8 +756,12 @@
 				},
 				"valueset": {
 					"allOf": [
-						{ "$ref": "#/definitions/type-schema-identifier" },
-						{ "$ref": "#/definitions/with-valueset-kind" }
+						{
+							"$ref": "#/definitions/type-schema-identifier"
+						},
+						{
+							"$ref": "#/definitions/with-valueset-kind"
+						}
 					]
 				},
 				"dependencies": {
@@ -455,7 +772,9 @@
 					}
 				}
 			},
-			"required": ["identifier"],
+			"required": [
+				"identifier"
+			],
 			"additionalProperties": false
 		}
 	]