diff --git a/src/ai-providers/agent-sdk/agent-sdk-provider.ts b/src/ai-providers/agent-sdk/agent-sdk-provider.ts
index 7cc1aa53..ec50fcbb 100644
--- a/src/ai-providers/agent-sdk/agent-sdk-provider.ts
+++ b/src/ai-providers/agent-sdk/agent-sdk-provider.ts
@@ -10,15 +10,17 @@
 
 import { resolve } from 'node:path'
 import type { Tool } from 'ai'
-import type { ProviderResult, ProviderEvent, AIProvider, GenerateInput, GenerateOpts } from '../types.js'
+import type { ProviderResult, ProviderEvent, AIProvider, GenerateOpts } from '../types.js'
+import type { SessionEntry } from '../../core/session.js'
 import type { AgentSdkConfig, AgentSdkOverride } from './query.js'
+import { toTextHistory } from '../../core/session.js'
+import { buildChatHistoryPrompt, DEFAULT_MAX_HISTORY } from '../utils.js'
 import { readAgentConfig } from '../../core/config.js'
 import { createChannel } from '../../core/async-channel.js'
 import { askAgentSdk } from './query.js'
 import { buildAgentSdkMcpServer } from './tool-bridge.js'
 
 export class AgentSdkProvider implements AIProvider {
-  readonly inputKind = 'text' as const
   readonly providerTag = 'agent-sdk' as const
 
   constructor(
@@ -49,8 +51,10 @@ export class AgentSdkProvider implements AIProvider {
     return { text: result.text, media: [] }
   }
 
-  async *generate(input: GenerateInput, opts?: GenerateOpts): AsyncGenerator<ProviderEvent> {
-    if (input.kind !== 'text') throw new Error('AgentSdkProvider expects text input')
+  async *generate(entries: SessionEntry[], prompt: string, opts?: GenerateOpts): AsyncGenerator<ProviderEvent> {
+    const maxHistory = opts?.maxHistoryEntries ?? DEFAULT_MAX_HISTORY
+    const textHistory = toTextHistory(entries).slice(-maxHistory)
+    const fullPrompt = buildChatHistoryPrompt(prompt, textHistory, opts?.historyPreamble)
 
     const config = await this.resolveConfig()
     const agentSdkConfig: AgentSdkConfig = {
@@ -58,7 +62,7 @@ export class AgentSdkProvider implements AIProvider {
       ...(opts?.disabledTools?.length
         ? { disallowedTools: [...(config.disallowedTools ?? []), ...opts.disabledTools] }
         : {}),
-      systemPrompt: input.systemPrompt ?? this.systemPrompt,
+      systemPrompt: opts?.systemPrompt ?? this.systemPrompt,
     }
 
     const override: AgentSdkOverride | undefined = opts?.agentSdk
@@ -67,7 +71,7 @@ export class AgentSdkProvider implements AIProvider {
     const channel = createChannel<ProviderEvent>()
 
     const resultPromise = askAgentSdk(
-      input.prompt,
+      fullPrompt,
       {
         ...agentSdkConfig,
         onToolUse: ({ id, name, input: toolInput }) => {
diff --git a/src/ai-providers/claude-code/claude-code-provider.ts b/src/ai-providers/claude-code/claude-code-provider.ts
index d53baf46..dd3a1f01 100644
--- a/src/ai-providers/claude-code/claude-code-provider.ts
+++ b/src/ai-providers/claude-code/claude-code-provider.ts
@@ -9,14 +9,16 @@
  */
 
 import { resolve } from 'node:path'
-import type { ProviderResult, ProviderEvent, AIProvider, GenerateInput, GenerateOpts } from '../types.js'
+import type { ProviderResult, ProviderEvent, AIProvider, GenerateOpts } from '../types.js'
+import type { SessionEntry } from '../../core/session.js'
 import type { ClaudeCodeConfig } from './types.js'
+import { toTextHistory } from '../../core/session.js'
+import { buildChatHistoryPrompt, DEFAULT_MAX_HISTORY } from '../utils.js'
 import { readAgentConfig } from '../../core/config.js'
 import { createChannel } from '../../core/async-channel.js'
 import { askClaudeCode } from './provider.js'
 
 export class ClaudeCodeProvider implements AIProvider {
-  readonly inputKind = 'text' as const
   readonly providerTag = 'claude-code' as const
 
   constructor(
@@ -39,8 +41,10 @@ export class ClaudeCodeProvider implements AIProvider {
     return { text: result.text, media: [] }
   }
 
-  async *generate(input: GenerateInput, opts?: GenerateOpts): AsyncGenerator<ProviderEvent> {
-    if (input.kind !== 'text') throw new Error('ClaudeCodeProvider expects text input')
+  async *generate(entries: SessionEntry[], prompt: string, opts?: GenerateOpts): AsyncGenerator<ProviderEvent> {
+    const maxHistory = opts?.maxHistoryEntries ?? DEFAULT_MAX_HISTORY
+    const textHistory = toTextHistory(entries).slice(-maxHistory)
+    const fullPrompt = buildChatHistoryPrompt(prompt, textHistory, opts?.historyPreamble)
 
     const config = await this.resolveConfig()
     const claudeCode: ClaudeCodeConfig = {
@@ -48,12 +52,12 @@ export class ClaudeCodeProvider implements AIProvider {
       ...(opts?.disabledTools?.length
         ? { disallowedTools: [...(config.disallowedTools ?? []), ...opts.disabledTools] }
         : {}),
-      systemPrompt: input.systemPrompt ?? this.systemPrompt,
+      systemPrompt: opts?.systemPrompt ?? this.systemPrompt,
     }
 
     const channel = createChannel<ProviderEvent>()
 
-    const resultPromise = askClaudeCode(input.prompt, {
+    const resultPromise = askClaudeCode(fullPrompt, {
       ...claudeCode,
       onToolUse: ({ id, name, input: toolInput }) => {
         channel.push({ type: 'tool_use', id, name, input: toolInput })
diff --git a/src/ai-providers/mock/index.ts b/src/ai-providers/mock/index.ts
index 75c3dc7e..39e61b0f 100644
--- a/src/ai-providers/mock/index.ts
+++ b/src/ai-providers/mock/index.ts
@@ -18,20 +18,21 @@
  *   expect(provider.askCalls).toHaveLength(0)
  */
 
-import type { AIProvider, ProviderEvent, ProviderResult, GenerateInput, GenerateOpts } from './types.js'
+import type { AIProvider, ProviderEvent, ProviderResult, GenerateOpts } from './types.js'
+import type { SessionEntry } from '../core/session.js'
 import type { MediaAttachment } from '../core/types.js'
 
 // ==================== Call Records ====================
 
 export interface MockAIProviderCall {
-  input: GenerateInput
+  entries: SessionEntry[]
+  prompt: string
   opts?: GenerateOpts
 }
 
 // ==================== Options ====================
 
 export interface MockAIProviderOpts {
-  inputKind?: 'text' | 'messages'
   providerTag?: 'vercel-ai' | 'claude-code' | 'agent-sdk'
   /** Text returned by ask(). Default: 'mock-ask-result'. */
   askResult?: string
@@ -40,7 +41,6 @@ export interface MockAIProviderOpts {
 // ==================== MockAIProvider ====================
 
 export class MockAIProvider implements AIProvider {
-  readonly inputKind: 'text' | 'messages'
   readonly providerTag: 'vercel-ai' | 'claude-code' | 'agent-sdk'
   readonly generateCalls: MockAIProviderCall[] = []
   readonly askCalls: string[] = []
@@ -50,7 +50,6 @@ export class MockAIProvider implements AIProvider {
     private events: ProviderEvent[],
     opts?: MockAIProviderOpts,
   ) {
-    this.inputKind = opts?.inputKind ?? 'messages'
     this.providerTag = opts?.providerTag ?? 'vercel-ai'
     this._askResult = opts?.askResult ?? 'mock-ask-result'
   }
@@ -60,8 +59,8 @@ export class MockAIProvider implements AIProvider {
     return { text: this._askResult, media: [] }
   }
 
-  async *generate(input: GenerateInput, opts?: GenerateOpts): AsyncIterable<ProviderEvent> {
-    this.generateCalls.push({ input, opts })
+  async *generate(entries: SessionEntry[], prompt: string, opts?: GenerateOpts): AsyncIterable<ProviderEvent> {
+    this.generateCalls.push({ entries, prompt, opts })
     for (const e of this.events) yield e
   }
 }
diff --git a/src/ai-providers/types.ts b/src/ai-providers/types.ts
index f5d24a82..0dd007df 100644
--- a/src/ai-providers/types.ts
+++ b/src/ai-providers/types.ts
@@ -1,4 +1,4 @@
-import type { ISessionStore, SDKModelMessage } from '../core/session.js'
+import type { ISessionStore, SessionEntry } from '../core/session.js'
 import type { CompactionConfig, CompactionResult } from '../core/compaction.js'
 import type { MediaAttachment } from '../core/types.js'
 
@@ -19,46 +19,39 @@ export interface ProviderResult {
   mediaUrls?: string[]
 }
 
-// ==================== GenerateProvider ====================
-
-/**
- * Input prepared by AgentCenter, dispatched by provider.inputKind.
- *
- * - 'text': Claude Code / Agent SDK — single string prompt with <chat_history> baked in.
- * - 'messages': Vercel AI SDK — structured ModelMessage[] (history carried natively).
- */
-export type GenerateInput =
-  | { kind: 'text'; prompt: string; systemPrompt?: string }
-  | { kind: 'messages'; messages: SDKModelMessage[]; systemPrompt?: string }
+// ==================== GenerateOpts ====================
 
 /** Per-request options passed through to the underlying provider. */
 export interface GenerateOpts {
+  /** System prompt override for this call. */
+  systemPrompt?: string
+  /** Preamble text for chat history (text providers only). */
+  historyPreamble?: string
+  /** Max history entries to include (text providers only). */
+  maxHistoryEntries?: number
   disabledTools?: string[]
   vercelAiSdk?: { provider: string; model: string; baseUrl?: string; apiKey?: string }
   agentSdk?: { model?: string; apiKey?: string; baseUrl?: string }
 }
 
+// ==================== AIProvider ====================
+
 /**
  * Slim provider interface — pure data-source adapter.
  *
- * Does NOT touch session management. AgentCenter prepares the input,
- * the provider calls the backend and yields ProviderEvents.
+ * Receives raw session entries + current prompt. Each provider decides
+ * how to serialize history for its backend (text string, structured messages, etc.).
  */
 export interface AIProvider {
-  /** Which input format this provider expects. */
-  readonly inputKind: 'text' | 'messages'
   /** Session log provenance tag. */
   readonly providerTag: 'vercel-ai' | 'claude-code' | 'agent-sdk'
   /** Stateless one-shot prompt (used for compaction summarization, etc.). */
   ask(prompt: string): Promise<ProviderResult>
   /** Stream events from the backend. Yields tool_use/tool_result/text, then done. */
-  generate(input: GenerateInput, opts?: GenerateOpts): AsyncIterable<ProviderEvent>
+  generate(entries: SessionEntry[], prompt: string, opts?: GenerateOpts): AsyncIterable<ProviderEvent>
   /**
    * Optional: custom compaction strategy. If implemented, AgentCenter delegates
    * compaction to the provider instead of using the default compactIfNeeded.
-   *
-   * Use case: providers with native server-side compaction (e.g. Anthropic API
-   * compact-2026-01-12) can bypass the local JSONL-based summarization.
    */
   compact?(session: ISessionStore, config: CompactionConfig): Promise<CompactionResult>
 }
diff --git a/src/ai-providers/vercel-ai-sdk/vercel-provider.spec.ts b/src/ai-providers/vercel-ai-sdk/vercel-provider.spec.ts
index ad97fced..22f2af56 100644
--- a/src/ai-providers/vercel-ai-sdk/vercel-provider.spec.ts
+++ b/src/ai-providers/vercel-ai-sdk/vercel-provider.spec.ts
@@ -92,9 +92,8 @@ describe('VercelAIProvider — per-request overrides', () => {
     mockCreateAgent.mockReturnValue(makeAgent() as any)
 
     // generate with disabledTools
-    const input = { kind: 'messages' as const, messages: [] }
     const events = []
-    for await (const e of provider.generate(input, { disabledTools: ['toolB'] })) {
+    for await (const e of provider.generate([], 'test', { disabledTools: ['toolB'] })) {
       events.push(e)
     }
 
@@ -113,8 +112,7 @@ describe('VercelAIProvider — per-request overrides', () => {
     mockCreateModelFromConfig.mockResolvedValue({ model: {} as any, key: 'gpt-4o' })
     mockCreateAgent.mockReturnValue(makeAgent() as any)
 
-    const input = { kind: 'messages' as const, messages: [] }
-    for await (const _ of provider.generate(input, { vercelAiSdk: { modelId: 'claude-3-7' } as any })) {
+    for await (const _ of provider.generate([], 'test', { vercelAiSdk: { modelId: 'claude-3-7' } as any })) {
       // drain
     }
 
@@ -122,30 +120,22 @@ describe('VercelAIProvider — per-request overrides', () => {
   })
 })
 
-// ==================== generate() input validation ====================
+// ==================== generate() behavior ====================
 
-describe('VercelAIProvider — generate() input', () => {
+describe('VercelAIProvider — generate()', () => {
   beforeEach(() => {
     vi.clearAllMocks()
     mockCreateModelFromConfig.mockResolvedValue({ model: {} as any, key: 'gpt-4o' })
     mockCreateAgent.mockReturnValue(makeAgent() as any)
   })
 
-  it('throws when input.kind is not "messages"', async () => {
-    const provider = makeProvider()
-    const input = { kind: 'text' as any, text: 'hello' }
-    const gen = provider.generate(input)
-    await expect(gen.next()).rejects.toThrow('expects messages input')
-  })
-
   it('yields done event with text from result', async () => {
     const provider = makeProvider()
     const agent = makeAgent('final answer')
     mockCreateAgent.mockReturnValue(agent as any)
 
-    const input = { kind: 'messages' as const, messages: [] }
     const events = []
-    for await (const e of provider.generate(input)) {
+    for await (const e of provider.generate([], 'test')) {
       events.push(e)
     }
 
@@ -158,9 +148,8 @@ describe('VercelAIProvider — generate() input', () => {
     mockCreateAgent.mockReturnValue(agent as any)
     const provider = makeProvider()
 
-    const input = { kind: 'messages' as const, messages: [] }
     await expect(async () => {
-      for await (const _ of provider.generate(input)) {
+      for await (const _ of provider.generate([], 'test')) {
         // drain
       }
     }).rejects.toThrow('model error')
diff --git a/src/ai-providers/vercel-ai-sdk/vercel-provider.ts b/src/ai-providers/vercel-ai-sdk/vercel-provider.ts
index aaaf1df1..a4ba59ea 100644
--- a/src/ai-providers/vercel-ai-sdk/vercel-provider.ts
+++ b/src/ai-providers/vercel-ai-sdk/vercel-provider.ts
@@ -7,16 +7,17 @@
  */
 
 import type { ModelMessage, Tool } from 'ai'
-import type { ProviderResult, ProviderEvent, AIProvider, GenerateInput, GenerateOpts } from '../types.js'
+import type { ProviderResult, ProviderEvent, AIProvider, GenerateOpts } from '../types.js'
+import type { SessionEntry } from '../../core/session.js'
 import type { Agent } from './agent.js'
 import type { MediaAttachment } from '../../core/types.js'
+import { toModelMessages } from '../../core/session.js'
 import { extractMediaFromToolOutput } from '../../core/media.js'
 import { createModelFromConfig, type ModelOverride } from './model-factory.js'
 import { createAgent } from './agent.js'
 import { createChannel } from '../../core/async-channel.js'
 
 export class VercelAIProvider implements AIProvider {
-  readonly inputKind = 'messages' as const
   readonly providerTag = 'vercel-ai' as const
   private cachedKey: string | null = null
   private cachedToolCount: number = 0
@@ -69,16 +70,16 @@ export class VercelAIProvider implements AIProvider {
     return { text: result.text ?? '', media }
   }
 
-  async *generate(input: GenerateInput, opts?: GenerateOpts): AsyncGenerator<ProviderEvent> {
-    if (input.kind !== 'messages') throw new Error('VercelAIProvider expects messages input')
+  async *generate(entries: SessionEntry[], _prompt: string, opts?: GenerateOpts): AsyncGenerator<ProviderEvent> {
+    const messages = toModelMessages(entries)
 
-    const agent = await this.resolveAgent(input.systemPrompt, opts?.disabledTools, opts?.vercelAiSdk)
+    const agent = await this.resolveAgent(opts?.systemPrompt, opts?.disabledTools, opts?.vercelAiSdk)
 
     const channel = createChannel<ProviderEvent>()
     const media: MediaAttachment[] = []
 
     const resultPromise = agent.generate({
-      messages: input.messages as ModelMessage[],
+      messages: messages as ModelMessage[],
       onStepFinish: (step) => {
         for (const tc of step.toolCalls) {
           channel.push({ type: 'tool_use', id: tc.toolCallId, name: tc.toolName, input: tc.input })
diff --git a/src/core/agent-center.ts b/src/core/agent-center.ts
index 8cbc4bb2..d320de4b 100644
--- a/src/core/agent-center.ts
+++ b/src/core/agent-center.ts
@@ -6,21 +6,21 @@
  *
  * Providers are slim data-source adapters; all shared logic lives here:
  *   - Session management (append, compact, read active)
- *   - Input format dispatch (text vs messages based on provider.inputKind)
  *   - Unified pipeline (logToolCall, stripImageData, extractMedia)
  *   - Message persistence (intermediate tool messages + final response)
+ *
+ * History serialization (text vs messages) is each provider's responsibility.
  */
 
 import type { AskOptions, ProviderResult, ProviderEvent, GenerateOpts } from './ai-provider-manager.js'
 import { GenerateRouter, StreamableResult } from './ai-provider-manager.js'
 import type { ISessionStore, ContentBlock } from './session.js'
-import { toTextHistory, toModelMessages } from './session.js'
 import type { CompactionConfig } from './compaction.js'
 import { compactIfNeeded } from './compaction.js'
 import type { MediaAttachment } from './types.js'
 import { extractMediaFromToolResultContent } from './media.js'
 import { persistMedia } from './media-store.js'
-import { logToolCall, stripImageData, buildChatHistoryPrompt, DEFAULT_MAX_HISTORY } from '../ai-providers/utils.js'
+import { logToolCall, stripImageData, DEFAULT_MAX_HISTORY } from '../ai-providers/utils.js'
 
 // ==================== Types ====================
 
@@ -65,9 +65,6 @@ export class AgentCenter {
     session: ISessionStore,
     opts?: AskOptions,
   ): AsyncGenerator<ProviderEvent> {
-    const maxHistory = opts?.maxHistoryEntries ?? this.defaultMaxHistory
-    const preamble = opts?.historyPreamble ?? this.defaultPreamble
-
     // 1. Append user message to session
     await session.appendUser(prompt, 'human')
 
@@ -86,28 +83,16 @@ export class AgentCenter {
     // 4. Read active window
     const entries = compactionResult.activeEntries ?? await session.readActive()
 
-    // 5. Build input based on provider.inputKind
+    // 5. Delegate to provider — each provider decides how to serialize history
     const genOpts: GenerateOpts = {
+      systemPrompt: opts?.systemPrompt,
+      historyPreamble: opts?.historyPreamble ?? this.defaultPreamble,
+      maxHistoryEntries: opts?.maxHistoryEntries ?? this.defaultMaxHistory,
       disabledTools: opts?.disabledTools,
       vercelAiSdk: opts?.vercelAiSdk,
       agentSdk: opts?.agentSdk,
     }
-
-    let source: AsyncIterable<ProviderEvent>
-    if (provider.inputKind === 'text') {
-      const textHistory = toTextHistory(entries).slice(-maxHistory)
-      const fullPrompt = buildChatHistoryPrompt(prompt, textHistory, preamble)
-      source = provider.generate(
-        { kind: 'text', prompt: fullPrompt, systemPrompt: opts?.systemPrompt },
-        genOpts,
-      )
-    } else {
-      const messages = toModelMessages(entries)
-      source = provider.generate(
-        { kind: 'messages', messages, systemPrompt: opts?.systemPrompt },
-        genOpts,
-      )
-    }
+    const source = provider.generate(entries, prompt, genOpts)
 
     // 6. Consume provider events — unified pipeline
     const media: MediaAttachment[] = []
diff --git a/src/core/ai-provider-manager.spec.ts b/src/core/ai-provider-manager.spec.ts
index 94213cd2..39b39775 100644
--- a/src/core/ai-provider-manager.spec.ts
+++ b/src/core/ai-provider-manager.spec.ts
@@ -132,7 +132,6 @@ describe('StreamableResult', () => {
 describe('GenerateRouter', () => {
   function makeProvider(tag: AIProvider['providerTag']): AIProvider {
     return {
-      inputKind: tag === 'vercel-ai' ? 'messages' : 'text',
       providerTag: tag,
       ask: vi.fn(async () => ({ text: `from-${tag}`, media: [] })),
       async *generate() { yield { type: 'done' as const, result: { text: '', media: [] } } },
diff --git a/src/core/ai-provider-manager.ts b/src/core/ai-provider-manager.ts
index fe6e63fe..7d7da37a 100644
--- a/src/core/ai-provider-manager.ts
+++ b/src/core/ai-provider-manager.ts
@@ -11,7 +11,7 @@ import type { ProviderEvent, ProviderResult, AIProvider } from '../ai-providers/
 
 export type {
   ProviderEvent, ProviderResult, AIProvider,
-  GenerateInput, GenerateOpts,
+  GenerateOpts,
 } from '../ai-providers/types.js'
 
 // ==================== StreamableResult ====================
diff --git a/src/core/session.spec.ts b/src/core/session.spec.ts
index 31cd33f6..72ac8991 100644
--- a/src/core/session.spec.ts
+++ b/src/core/session.spec.ts
@@ -74,8 +74,11 @@ describe('toModelMessages', () => {
         { type: 'text', text: 'thinking...' },
         { type: 'tool_use', id: 't1', name: 'Read', input: { path: '/tmp' } },
       ]),
+      userBlocks([
+        { type: 'tool_result', tool_use_id: 't1', content: 'file contents' },
+      ]),
     ])
-    expect(msgs).toHaveLength(1)
+    expect(msgs).toHaveLength(2)
     expect(msgs[0].role).toBe('assistant')
     const content = (msgs[0] as { content: unknown[] }).content
     expect(content).toHaveLength(2)
@@ -144,6 +147,42 @@ describe('toModelMessages', () => {
     expect(msgs[2].role).toBe('tool')
     expect(msgs[3].role).toBe('assistant')
   })
+
+  it('should strip orphaned tool-call entries that have no matching tool-result', () => {
+    const msgs = toModelMessages([
+      userText('do two things'),
+      // Assistant calls two tools, but only one result exists
+      assistantBlocks([
+        { type: 'tool_use', id: 't1', name: 'ToolA', input: {} },
+        { type: 'tool_use', id: 't2', name: 'ToolB', input: {} },
+      ]),
+      // Only t1 has a result — t2 is orphaned (e.g. session interrupted)
+      userBlocks([
+        { type: 'tool_result', tool_use_id: 't1', content: 'result A' },
+      ]),
+      assistantText('done'),
+    ])
+    // Assistant message should only contain the tool-call for t1
+    expect(msgs).toHaveLength(4)
+    const assistantContent = (msgs[1] as { content: unknown[] }).content
+    expect(assistantContent).toHaveLength(1)
+    expect((assistantContent[0] as { toolCallId: string }).toolCallId).toBe('t1')
+  })
+
+  it('should drop assistant message entirely if all tool-calls are orphaned', () => {
+    const msgs = toModelMessages([
+      userText('hi'),
+      // Assistant only has tool_use, no results exist at all
+      assistantBlocks([
+        { type: 'tool_use', id: 'orphan1', name: 'Missing', input: {} },
+      ]),
+      assistantText('recovered'),
+    ])
+    // The orphaned assistant message should be dropped
+    expect(msgs).toHaveLength(2)
+    expect(msgs[0]).toEqual({ role: 'user', content: 'hi' })
+    expect(msgs[1]).toEqual({ role: 'assistant', content: 'recovered' })
+  })
 })
 
 // ==================== toTextHistory ====================
diff --git a/src/core/session.ts b/src/core/session.ts
index 7eeab828..cb2e8499 100644
--- a/src/core/session.ts
+++ b/src/core/session.ts
@@ -375,7 +375,39 @@ export function toModelMessages(entries: SessionEntry[]): SDKModelMessage[] {
     // system role messages (non-boundary) are skipped — they don't map to SDK messages
   }
 
-  return messages
+  // Sanitize: remove tool-call entries that have no matching tool-result.
+  // This can happen when compaction truncates between a tool_use and its result,
+  // or when a session was interrupted mid-tool-call.
+  return sanitizeToolMessages(messages)
+}
+
+/** Strip orphaned tool-call entries that have no matching tool-result downstream. */
+function sanitizeToolMessages(messages: SDKModelMessage[]): SDKModelMessage[] {
+  // Collect all tool-result IDs
+  const resultIds = new Set<string>()
+  for (const msg of messages) {
+    if (msg.role === 'tool') {
+      for (const part of msg.content) {
+        resultIds.add(part.toolCallId)
+      }
+    }
+  }
+
+  const out: SDKModelMessage[] = []
+  for (const msg of messages) {
+    if (msg.role === 'assistant' && Array.isArray(msg.content)) {
+      const filtered = msg.content.filter(
+        (part) => part.type !== 'tool-call' || resultIds.has(part.toolCallId),
+      )
+      if (filtered.length > 0) {
+        out.push({ ...msg, content: filtered })
+      }
+      // Drop assistant message entirely if only orphaned tool-calls remained
+    } else {
+      out.push(msg)
+    }
+  }
+  return out
 }
 
 /** Max characters for a tool input/output summary line. */