diff --git a/CHANGELOG.md b/CHANGELOG.md
index f3a6080ec..8c7be2032 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,15 +21,25 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 - `refactor(llm)`: `OpenAiProvider::generation_params()` private helper extracted; removes 4
   duplicate `generation_overrides` tuple expansions in `send_request`, `send_stream_request`,
   `debug_request_json`, and `chat_with_tools`. (#4873)
+- `build(acp)`: bump `agent-client-protocol` 0.12.1 → 0.14.0 and `agent-client-protocol-schema` = 0.13.6; remove dead `agent-client-protocol-tokio` dependency
+- `feat(acp)`: `unstable-session-usage` feature now maps to upstream `unstable_end_turn_token_usage` gate (renamed, not stabilized in 0.14.0)
+- `feat(acp)`: `unstable-elicitation` feature now also enables `agent-client-protocol/unstable_elicitation` core passthrough for `elicitation/create` handler wiring
+- `refactor(acp)`: provider ext-method types renamed to singular: `SetProvidersRequest/Response` → `SetProviderRequest/Response`, `DisableProvidersRequest/Response` → `DisableProviderRequest/Response`
+- `refactor(acp)`: logout, session/close, session/delete, session/resume, and additional-directories handlers are now unconditional (feature flags retained as no-op tombstones for workspace forwarding compatibility)
+
+### Removed
+
+- `refactor(acp)`: `session/set_model` dedicated RPC method removed (deleted upstream in 0.14.0); model switching remains fully available via `session/set_config_option` (config_id="model") and the `$/model` slash command
+- `refactor(acp)`: inbound/outbound message-id echo removed (`PromptRequest.message_id` and `PromptResponse.user_message_id` were removed upstream in 0.14.0)
+
+### Fixed
+
 - `refactor(llm)`: `parse_gemini_error` in `zeph-llm` now delegates the base `ApiError` and
   `ContextLengthExceeded` construction to `crate::http::map_error_response`, consistent with all
   other backends (claude, openai, gonka, cocoon). Gemini-specific `RESOURCE_EXHAUSTED → RateLimited`
   handling is preserved. (#4868)
 - refactor(memory): remove `ScoredCandidate` single-field wrapper in `tiered_retrieval.rs` ([#4867](https://github.com/bug-ops/zeph/issues/4867))
 - fix(memory): replace `.entered()` span guard with removal in `tiered_retrieval.rs` async fn ([#4866](https://github.com/bug-ops/zeph/issues/4866))
-
-### Fixed
-
 - `docs(config)`: `CandleConfig` in `zeph-config` now has a `///` doc comment describing its
   purpose (`[llm.candle]` TOML section) and its relationship to `CandleInlineConfig`. (#4869)
 
diff --git a/Cargo.lock b/Cargo.lock
index 7dc398e7b..a97e43a21 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -92,58 +92,31 @@ dependencies = [
 
 [[package]]
 name = "agent-client-protocol"
-version = "0.11.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2af62fb84df2af0f933d8f5fd78b843fa5eb0ec5a48fa1b528c41951d0bbe36c"
-dependencies = [
- "agent-client-protocol-derive",
- "agent-client-protocol-schema 0.12.0",
- "anyhow",
- "futures",
- "futures-concurrency",
- "jsonrpcmsg",
- "rmcp",
- "rustc-hash 2.1.2",
- "schemars 1.2.1",
- "serde",
- "serde_json",
- "thiserror 2.0.18",
- "tokio",
- "tokio-util",
- "tracing",
- "uuid",
-]
-
-[[package]]
-name = "agent-client-protocol"
-version = "0.12.1"
+version = "0.14.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4361ba6627e51de955b10f3c77fb9eb959c85191a236c1c2c84e32f4ff240faf"
+checksum = "5efba6592048ef8a9ac97de8d79b2d9933d8ac4d94f7a2de102348fed0c61103"
 dependencies = [
  "agent-client-protocol-derive",
- "agent-client-protocol-schema 0.13.2",
+ "agent-client-protocol-schema",
  "async-process",
  "blocking",
  "futures",
  "futures-concurrency",
  "jsonrpcmsg",
- "rmcp",
  "rustc-hash 2.1.2",
  "schemars 1.2.1",
  "serde",
  "serde_json",
  "shell-words",
- "tokio",
- "tokio-util",
  "tracing",
  "uuid",
 ]
 
 [[package]]
 name = "agent-client-protocol-derive"
-version = "0.11.1"
+version = "0.14.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cabdc9d845d08ec7ed2d0c9de1ae4a1b198301407d55855261572761be90ec9f"
+checksum = "4d176a10d4cb06e0262a738c3c5bf21ff0968db13a666e31cbca94a3d3d72e7c"
 dependencies = [
  "quote",
  "syn 2.0.117",
@@ -151,9 +124,9 @@ dependencies = [
 
 [[package]]
 name = "agent-client-protocol-schema"
-version = "0.12.0"
+version = "0.13.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "49bae57dad1c28a362fbdcf7bab0583316a02b45a70792109fced55780a3b63c"
+checksum = "c290bfa00c6b52339db66f8e9cf711d5f08530800529f7d619ff24d6cba253d0"
 dependencies = [
  "anyhow",
  "derive_more 2.1.1",
@@ -165,37 +138,6 @@ dependencies = [
  "tracing",
 ]
 
-[[package]]
-name = "agent-client-protocol-schema"
-version = "0.13.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b957d8391ac3933e2a940446171c508d2b8ffc386d8fa7d0b9c936a2575b463e"
-dependencies = [
- "anyhow",
- "derive_more 2.1.1",
- "schemars 1.2.1",
- "serde",
- "serde_json",
- "serde_with",
- "strum 0.28.0",
- "tracing",
-]
-
-[[package]]
-name = "agent-client-protocol-tokio"
-version = "0.11.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0e1572b219f22c4b3be0f20f934c8b6f1d1457126ce72923c4f6608f96153b65"
-dependencies = [
- "agent-client-protocol 0.11.1",
- "futures",
- "serde",
- "serde_json",
- "shell-words",
- "tokio",
- "tokio-util",
-]
-
 [[package]]
 name = "ahash"
 version = "0.8.12"
@@ -4872,7 +4814,7 @@ version = "5.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "51e219e79014df21a225b1860a479e2dcd7cbd9130f4defd4bd0e191ea31d67d"
 dependencies = [
- "base64 0.22.1",
+ "base64 0.21.7",
  "chrono",
  "getrandom 0.2.17",
  "http",
@@ -10582,9 +10524,8 @@ dependencies = [
 name = "zeph-acp"
 version = "0.21.4"
 dependencies = [
- "agent-client-protocol 0.12.1",
- "agent-client-protocol-schema 0.13.2",
- "agent-client-protocol-tokio",
+ "agent-client-protocol",
+ "agent-client-protocol-schema",
  "async-stream",
  "axum 0.8.9",
  "base64 0.22.1",
diff --git a/Cargo.toml b/Cargo.toml
index e06d03a35..7b2455a70 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -17,9 +17,8 @@ publish = true
 
 [workspace.dependencies]
 age = { version = "0.11.3", default-features = false }
-agent-client-protocol = "0.12.1"
-agent-client-protocol-schema = "0.13.2"
-agent-client-protocol-tokio = "0.11.1"
+agent-client-protocol = "0.14.0"
+agent-client-protocol-schema = "=0.13.6"
 anyhow = "1.0.102"
 arboard = "3.6.1"
 arc-swap = "1.9.1"
diff --git a/crates/zeph-acp/Cargo.toml b/crates/zeph-acp/Cargo.toml
index fc44c5a06..6e7090080 100644
--- a/crates/zeph-acp/Cargo.toml
+++ b/crates/zeph-acp/Cargo.toml
@@ -17,31 +17,32 @@ default = [
     "unstable-session-delete",
     "unstable-session-fork",
     "unstable-session-usage",
-    "unstable-session-model",
     "unstable-logout",
     "unstable-elicitation",
     "unstable-llm-providers",
 ]
 acp-http = ["dep:axum", "dep:blake3", "dep:dashmap", "dep:async-stream", "dep:tower-http", "dep:subtle", "dep:tower"]
-# session/close is now exposed as session/delete in acp 0.12.1
-unstable-session-delete = ["agent-client-protocol/unstable_session_delete"]
+# session/close and session/delete stabilized in acp 0.14.0; no upstream feature gate needed
+unstable-session-delete = []
 unstable-session-fork = ["agent-client-protocol/unstable_session_fork"]
 # session/resume is stable in acp 0.12.1; no feature gate needed
 unstable-session-resume = []
-unstable-session-usage = ["agent-client-protocol/unstable_session_usage"]
-unstable-session-model = ["agent-client-protocol/unstable_session_model"]
-unstable-elicitation = ["dep:agent-client-protocol-schema", "agent-client-protocol-schema/unstable_elicitation"]
+# renamed from unstable_session_usage in acp 0.14.0; Usage struct + PromptResponse.usage remain gated
+unstable-session-usage = ["agent-client-protocol/unstable_end_turn_token_usage"]
+unstable-elicitation = ["dep:agent-client-protocol-schema", "agent-client-protocol-schema/unstable_elicitation", "agent-client-protocol/unstable_elicitation"]
 unstable-llm-providers = ["dep:agent-client-protocol-schema", "agent-client-protocol-schema/unstable_llm_providers"]
-unstable-logout = ["agent-client-protocol/unstable_logout"]
+# logout stabilized in acp 0.13.0; no upstream feature gate needed
+unstable-logout = []
 unstable-auth-methods = ["agent-client-protocol/unstable_auth_methods"]
 unstable-boolean-config = ["agent-client-protocol/unstable_boolean_config"]
-unstable-message-id = ["agent-client-protocol/unstable_message_id"]
-unstable-session-add-dirs = ["agent-client-protocol/unstable_session_additional_directories"]
+# message-id stabilized in acp 0.14.0; no upstream feature gate needed
+unstable-message-id = []
+# session-add-dirs stabilized in acp 0.14.0; no upstream feature gate needed
+unstable-session-add-dirs = []
 
 [dependencies]
 agent-client-protocol = { workspace = true }
 agent-client-protocol-schema = { workspace = true, optional = true }
-agent-client-protocol-tokio = { workspace = true }
 async-stream = { workspace = true, optional = true }
 axum = { workspace = true, features = ["ws"], optional = true }
 base64.workspace = true
diff --git a/crates/zeph-acp/README.md b/crates/zeph-acp/README.md
index 8c77a1274..7032cbe31 100644
--- a/crates/zeph-acp/README.md
+++ b/crates/zeph-acp/README.md
@@ -363,7 +363,6 @@ The `initialize` response includes an `auth_hint` key in its metadata map. For s
 | `unstable-session-fork` | unstable | Enables the `fork_session` ACP method. See below. |
 | `unstable-session-resume` | unstable | Enables the `resume_session` ACP method. See below. |
 | `unstable-session-usage` | unstable | Enables `UsageUpdate` events — token counts (input, output, cache) sent to the IDE after each turn. See below. |
-| `unstable-session-model` | unstable | Enables `SetSessionModel` — IDE-driven model switching via a native picker without `session/configure`. See below. |
 | `unstable-session-info-update` | unstable | Enables `SessionInfoUpdate` — agent-generated session title emitted to the IDE after the first turn. See below. |
 | `unstable-elicitation` | unstable | Exposes elicitation schema types (`ElicitationRequest`, etc.) for future agent-loop integration. SDK methods not yet available in 0.10.3. |
 | `unstable-logout` | unstable | Enables the `logout` ACP method and advertises `auth.logout` capability. Zeph logout is a no-op (vault-based auth). |
@@ -379,7 +378,6 @@ zeph-acp = { version = "*", features = [
     "unstable-session-fork",
     "unstable-session-resume",
     "unstable-session-usage",
-    "unstable-session-model",
     "unstable-session-info-update",
     "unstable-elicitation",
     "unstable-logout",
@@ -423,16 +421,6 @@ Enables `UsageUpdate` session events. After each agent turn `ZephAcpAgent` emits
 
 The IDE can use this data to display running cost estimates or token budgets without polling a separate endpoint.
 
-### `unstable-session-model`
-
-Enables `SetSessionModel` handling. When the IDE sends a `set_session_model` request (e.g., from a native model-picker dropdown), `ZephAcpAgent`:
-
-1. Resolves the requested `"provider:model"` key via `ProviderFactory`.
-2. Stores the resolved provider in the session-scoped `provider_override`.
-3. Returns a confirmation to the IDE so the picker reflects the active selection.
-
-This avoids the need to wrap model selection in a `session/configure` call and maps directly to the Zed AI model picker interaction.
-
 ### `unstable-session-info-update`
 
 Enables `SessionInfoUpdate` events. After the first completed turn in a new session, `ZephAcpAgent` emits a `SessionUpdate::SessionInfoUpdate` containing a short, LLM-generated title derived from the opening message. The IDE can use this title to label the session in its sidebar or tab bar.
diff --git a/crates/zeph-acp/src/agent/handlers/mod.rs b/crates/zeph-acp/src/agent/handlers/mod.rs
index ab5fcedf8..4ca884154 100644
--- a/crates/zeph-acp/src/agent/handlers/mod.rs
+++ b/crates/zeph-acp/src/agent/handlers/mod.rs
@@ -1,14 +1,9 @@
 // SPDX-FileCopyrightText: 2026 Andrei G <bug-ops>
 // SPDX-License-Identifier: MIT OR Apache-2.0
 
-// Handler stubs for ACP 0.11 migration. Implementations land in PR 2 (#3267).
-// See .local/plan/acp-migration-plan.md §4 Steps 3–4 for the full contract.
-
 pub(crate) mod authenticate;
 pub(crate) mod cancel;
-#[cfg(feature = "unstable-session-delete")]
 pub(crate) mod close_session;
-#[cfg(feature = "unstable-session-delete")]
 pub(crate) mod delete_session;
 pub(crate) mod dispatch;
 #[cfg(feature = "unstable-session-fork")]
@@ -16,13 +11,9 @@ pub(crate) mod fork_session;
 pub(crate) mod initialize;
 pub(crate) mod list_sessions;
 pub(crate) mod load_session;
-#[cfg(feature = "unstable-logout")]
 pub(crate) mod logout;
 pub(crate) mod new_session;
 pub(crate) mod prompt;
-#[cfg(feature = "unstable-session-resume")]
 pub(crate) mod resume_session;
 pub(crate) mod set_session_config_option;
 pub(crate) mod set_session_mode;
-#[cfg(feature = "unstable-session-model")]
-pub(crate) mod set_session_model;
diff --git a/crates/zeph-acp/src/agent/handlers/set_session_model.rs b/crates/zeph-acp/src/agent/handlers/set_session_model.rs
deleted file mode 100644
index c7a37cbe9..000000000
--- a/crates/zeph-acp/src/agent/handlers/set_session_model.rs
+++ /dev/null
@@ -1,21 +0,0 @@
-// SPDX-FileCopyrightText: 2026 Andrei G <bug-ops>
-// SPDX-License-Identifier: MIT OR Apache-2.0
-
-//! Handler for `session/set_model` (feature `unstable-session-model`).
-
-use std::sync::Arc;
-
-use agent_client_protocol as acp;
-
-use crate::agent::ZephAcpAgentState;
-
-/// Handle an ACP `session/set_model` request.
-pub(crate) async fn handle_set_session_model(
-    req: acp::schema::SetSessionModelRequest,
-    responder: acp::Responder<acp::schema::SetSessionModelResponse>,
-    _cx: acp::ConnectionTo<acp::Client>,
-    state: Arc<ZephAcpAgentState>,
-) -> acp::Result<()> {
-    let resp = state.do_set_session_model(req).await?;
-    responder.respond(resp)
-}
diff --git a/crates/zeph-acp/src/agent/mod.rs b/crates/zeph-acp/src/agent/mod.rs
index ed6a202b0..08be9de7c 100644
--- a/crates/zeph-acp/src/agent/mod.rs
+++ b/crates/zeph-acp/src/agent/mod.rs
@@ -11,6 +11,7 @@
 //! IDE capabilities (filesystem, terminal, LSP) are detected during `initialize()` and
 //! surfaced to the agent loop through [`AcpContext`].
 
+#[cfg(feature = "unstable-llm-providers")]
 use std::collections::{HashMap, HashSet};
 use std::path::{Component, PathBuf};
 use std::pin::Pin;
@@ -22,6 +23,7 @@ use parking_lot::{Mutex, RwLock};
 use agent_client_protocol as acp;
 use futures::StreamExt as _;
 use tokio::sync::{mpsc, oneshot};
+#[cfg(feature = "unstable-elicitation")]
 use tokio::task::JoinHandle;
 use tokio_util::sync::CancellationToken;
 use zeph_core::channel::{ChannelMessage, LoopbackChannel, LoopbackHandle};
@@ -471,13 +473,6 @@ pub(crate) struct SessionEntry {
     /// after `tool_call_update` notifications are sent (ACP requires the terminal to
     /// remain alive until after the notification that embeds it).
     pub(crate) shell_executor: Option<AcpShellExecutor>,
-    /// Message-id captured at the start of a `do_prompt` turn.
-    ///
-    /// The existing one-in-flight-prompt invariant (enforced by `output_rx.lock().take()` at
-    /// line ~1142) guarantees at most one concurrent writer, so a plain `Mutex<Option<String>>`
-    /// is sufficient without `parking_lot`.
-    #[cfg(feature = "unstable-message-id")]
-    pub(crate) current_message_id: std::sync::Mutex<Option<String>>,
     /// Join handle for the elicitation bridge task spawned in `do_new_session`.
     ///
     /// Aborted on session close / reap for clean shutdown. `None` when the IDE
@@ -566,8 +561,6 @@ pub struct ZephAcpAgentState {
     additional_directories_allow: Vec<std::path::PathBuf>,
     /// Auth methods to advertise in the `initialize` response. MVP: always `[Agent]`.
     auth_methods_config: Vec<zeph_core::config::AcpAuthMethod>,
-    /// When `true`, echo `PromptRequest.message_id` through responses and chunks.
-    message_ids_enabled: bool,
     /// Timeout configuration for ACP operations (terminal, elicitation, MCP bridge).
     pub(crate) timeouts: zeph_config::AcpTimeoutsConfig,
     /// Whether the IDE advertised elicitation capability during `initialize()`.
@@ -620,7 +613,6 @@ impl ZephAcpAgentState {
             reaper_cancel: CancellationToken::new(),
             additional_directories_allow: Vec::new(),
             auth_methods_config: vec![zeph_core::config::AcpAuthMethod::Agent],
-            message_ids_enabled: true,
             timeouts: zeph_config::AcpTimeoutsConfig::default(),
             #[cfg(feature = "unstable-elicitation")]
             elicitation_supported: std::sync::atomic::AtomicBool::new(false),
@@ -653,13 +645,6 @@ impl ZephAcpAgentState {
         self
     }
 
-    /// Configure message-id echo behaviour.
-    #[must_use]
-    pub fn with_message_ids_enabled(mut self, enabled: bool) -> Self {
-        self.message_ids_enabled = enabled;
-        self
-    }
-
     /// Configure ACP operation timeouts.
     #[must_use]
     pub fn with_timeouts(mut self, timeouts: zeph_config::AcpTimeoutsConfig) -> Self {
@@ -1141,7 +1126,6 @@ impl ZephAcpAgentState {
         let caps = {
             let mut session_caps = acp::schema::SessionCapabilities::new();
             session_caps = session_caps.list(acp::schema::SessionListCapabilities::default());
-            #[cfg(feature = "unstable-session-delete")]
             {
                 session_caps = session_caps.close(acp::schema::SessionCloseCapabilities::default());
             }
@@ -1149,7 +1133,6 @@ impl ZephAcpAgentState {
             {
                 session_caps = session_caps.fork(acp::schema::SessionForkCapabilities::default());
             }
-            #[cfg(feature = "unstable-session-resume")]
             {
                 session_caps =
                     session_caps.resume(acp::schema::SessionResumeCapabilities::default());
@@ -1157,7 +1140,6 @@ impl ZephAcpAgentState {
             caps.session_capabilities(session_caps)
         };
 
-        #[cfg(feature = "unstable-logout")]
         let caps = caps.auth(
             acp::schema::AgentAuthCapabilities::default()
                 .logout(acp::schema::LogoutCapabilities::default()),
@@ -1227,8 +1209,7 @@ impl ZephAcpAgentState {
         Ok(acp::schema::AuthenticateResponse::default())
     }
 
-    #[cfg(feature = "unstable-logout")]
-    #[allow(clippy::unused_async, dead_code)]
+    #[allow(clippy::unused_async)]
     #[tracing::instrument(skip_all, name = "acp.handler.logout")]
     pub(crate) async fn do_logout(
         &self,
@@ -1333,7 +1314,6 @@ impl ZephAcpAgentState {
         args: acp::schema::NewSessionRequest,
         cx: &acp::ConnectionTo<acp::Client>,
     ) -> acp::Result<acp::schema::NewSessionResponse> {
-        #[cfg(feature = "unstable-session-add-dirs")]
         self.validate_additional_directories(&args.additional_directories)?;
         self.evict_oldest_idle_session_if_full()?;
 
@@ -1375,6 +1355,7 @@ impl ZephAcpAgentState {
         );
         let shell_executor = acp_ctx.shell_executor.clone();
         let initial_model = self.initial_model();
+        #[cfg_attr(not(feature = "unstable-elicitation"), allow(unused_mut))]
         let mut entry = Self::make_session_entry(
             handle,
             initial_model.clone(),
@@ -1425,11 +1406,9 @@ impl ZephAcpAgentState {
     /// Take the `input_tx` / `output_rx` pair for a session and mark it as active.
     ///
     /// Returns an error when the session does not exist or a prompt is already in flight.
-    /// Also writes `turn_message_id` into the per-session slot when the feature is enabled.
     fn acquire_prompt_channels(
         &self,
         session_id: &acp::schema::SessionId,
-        #[cfg(feature = "unstable-message-id")] turn_message_id: Option<&str>,
     ) -> acp::Result<(mpsc::Sender<ChannelMessage>, mpsc::Receiver<LoopbackEvent>)> {
         let sessions = self.sessions.lock();
         let entry = sessions
@@ -1441,14 +1420,6 @@ impl ZephAcpAgentState {
             .take()
             .ok_or_else(|| acp::Error::internal_error().data("prompt already in progress"))?;
         entry.touch();
-        // Write message_id here — output_rx take succeeded, prompt will proceed.
-        #[cfg(feature = "unstable-message-id")]
-        if let Some(mid) = turn_message_id {
-            *entry
-                .current_message_id
-                .lock()
-                .unwrap_or_else(std::sync::PoisonError::into_inner) = Some(mid.to_owned());
-        }
         Ok((entry.input_tx.clone(), rx))
     }
 
@@ -1472,15 +1443,6 @@ impl ZephAcpAgentState {
     ) -> acp::Result<acp::schema::PromptResponse> {
         tracing::debug!(session_id = %args.session_id, "ACP prompt");
 
-        // Capture message_id; written to per-session slot only AFTER output_rx take succeeds
-        // to prevent stale id from leaking when a prompt is rejected as "already in progress".
-        #[cfg(feature = "unstable-message-id")]
-        let turn_message_id: Option<String> = if self.message_ids_enabled {
-            args.message_id.clone()
-        } else {
-            None
-        };
-
         // Capture session cwd for file:// boundary enforcement.
         let session_cwd = self
             .sessions
@@ -1500,11 +1462,7 @@ impl ZephAcpAgentState {
                 .await;
         }
 
-        let (input_tx, output_rx) = self.acquire_prompt_channels(
-            &args.session_id,
-            #[cfg(feature = "unstable-message-id")]
-            turn_message_id.as_deref(),
-        )?;
+        let (input_tx, output_rx) = self.acquire_prompt_channels(&args.session_id)?;
 
         self.persist_user_message_async(&args.session_id, text.clone());
 
@@ -1542,18 +1500,7 @@ impl ZephAcpAgentState {
             self.maybe_generate_session_title(&args.session_id, &text);
         }
 
-        // Clear per-turn message-id slot now that the turn is complete.
-        #[cfg(feature = "unstable-message-id")]
-        if let Some(entry) = self.sessions.lock().get(&args.session_id) {
-            *entry
-                .current_message_id
-                .lock()
-                .unwrap_or_else(std::sync::PoisonError::into_inner) = None;
-        }
-
         Ok(build_prompt_response(
-            #[cfg(feature = "unstable-message-id")]
-            turn_message_id.as_deref(),
             stop_reason,
             #[cfg(feature = "unstable-session-usage")]
             drain.turn_usage,
@@ -1570,8 +1517,6 @@ impl ZephAcpAgentState {
         Ok(())
     }
 
-    #[cfg(feature = "unstable-session-delete")]
-    #[allow(dead_code)]
     #[tracing::instrument(skip_all, name = "acp.handler.close_session", fields(session_id = %args.session_id))]
     pub(crate) async fn do_close_session(
         &self,
@@ -1610,8 +1555,7 @@ impl ZephAcpAgentState {
         Ok(acp::schema::CloseSessionResponse::default())
     }
 
-    #[cfg(feature = "unstable-session-delete")]
-    #[allow(clippy::unused_async, dead_code)]
+    #[allow(clippy::unused_async)]
     #[tracing::instrument(skip_all, name = "acp.handler.delete_session", fields(session_id = %args.session_id))]
     pub(crate) async fn do_delete_session(
         &self,
@@ -1632,7 +1576,6 @@ impl ZephAcpAgentState {
         args: acp::schema::LoadSessionRequest,
         cx: &acp::ConnectionTo<acp::Client>,
     ) -> acp::Result<acp::schema::LoadSessionResponse> {
-        #[cfg(feature = "unstable-session-add-dirs")]
         self.validate_additional_directories(&args.additional_directories)?;
         if self.sessions.lock().contains_key(&args.session_id) {
             return Ok(acp::schema::LoadSessionResponse::new());
@@ -1780,7 +1723,6 @@ impl ZephAcpAgentState {
         args: acp::schema::ForkSessionRequest,
         cx: &acp::ConnectionTo<acp::Client>,
     ) -> acp::Result<acp::schema::ForkSessionResponse> {
-        #[cfg(feature = "unstable-session-add-dirs")]
         self.validate_additional_directories(&args.additional_directories)?;
         let in_memory = self.sessions.lock().contains_key(&args.session_id);
 
@@ -1883,15 +1825,12 @@ impl ZephAcpAgentState {
         Ok(resp)
     }
 
-    #[cfg(feature = "unstable-session-resume")]
-    #[allow(dead_code)]
     #[tracing::instrument(skip_all, name = "acp.handler.resume_session")]
     pub(crate) async fn do_resume_session(
         &self,
         args: acp::schema::ResumeSessionRequest,
         cx: &acp::ConnectionTo<acp::Client>,
     ) -> acp::Result<acp::schema::ResumeSessionResponse> {
-        #[cfg(feature = "unstable-session-add-dirs")]
         self.validate_additional_directories(&args.additional_directories)?;
         if self.sessions.lock().contains_key(&args.session_id) {
             return Ok(acp::schema::ResumeSessionResponse::new());
@@ -2087,7 +2026,6 @@ impl ZephAcpAgentState {
     /// Each requested path is canonicalized and checked with `Path::starts_with` (component-aware)
     /// against every entry in `self.additional_directories_allow`. Returns an `invalid_params`
     /// error if any path is not covered by the allowlist.
-    #[cfg(feature = "unstable-session-add-dirs")]
     fn validate_additional_directories(
         &self,
         requested: &[std::path::PathBuf],
@@ -2119,53 +2057,6 @@ impl ZephAcpAgentState {
         }
         Ok(out)
     }
-
-    #[cfg(feature = "unstable-session-model")]
-    #[allow(clippy::unused_async, dead_code)]
-    #[tracing::instrument(skip_all, name = "acp.handler.set_session_model")]
-    pub(crate) async fn do_set_session_model(
-        &self,
-        args: acp::schema::SetSessionModelRequest,
-    ) -> acp::Result<acp::schema::SetSessionModelResponse> {
-        let model_id: &str = &args.model_id.0;
-
-        let Some(ref factory) = self.provider_factory else {
-            return Err(acp::Error::internal_error().data("model switching not configured"));
-        };
-
-        if !self
-            .available_models_snapshot()
-            .iter()
-            .any(|m| m == model_id)
-        {
-            return Err(acp::Error::invalid_request().data("model not in allowed list"));
-        }
-
-        let Some(new_provider) = factory(model_id) else {
-            return Err(acp::Error::invalid_request().data("unknown model"));
-        };
-
-        {
-            let sessions = self.sessions.lock();
-            let entry = sessions
-                .get(&args.session_id)
-                .ok_or_else(|| acp::Error::internal_error().data("session not found"))?;
-            *entry.provider_override.write() = Some(new_provider);
-            model_id.clone_into(&mut *entry.current_model.lock());
-        }
-
-        tracing::debug!(session_id = %args.session_id, model = %model_id, "ACP session model switched via set_session_model");
-
-        let info_update = acp::schema::SessionUpdate::SessionInfoUpdate(
-            acp::schema::SessionInfoUpdate::new().meta(model_meta(model_id)),
-        );
-        self.send_notification_nowait(
-            &args.session_id,
-            acp::schema::SessionNotification::new(args.session_id.clone(), info_update),
-        );
-
-        Ok(acp::schema::SetSessionModelResponse::new())
-    }
 }
 
 impl ZephAcpAgentState {
@@ -2545,13 +2436,6 @@ impl ZephAcpAgentState {
         // Per-turn token totals for PromptResponse.usage (separate from session accumulator).
         #[cfg(feature = "unstable-session-usage")]
         let mut turn_usage = TurnUsage::default();
-        // Capture turn message_id once per drain to avoid re-locking sessions per event.
-        #[cfg(feature = "unstable-message-id")]
-        let turn_mid: Option<String> = self
-            .sessions
-            .lock()
-            .get(session_id)
-            .and_then(|e| e.current_message_id.lock().ok().and_then(|g| g.clone()));
         loop {
             let event = if let Some(ref signal) = cancel_signal {
                 tokio::select! {
@@ -2608,10 +2492,6 @@ impl ZephAcpAgentState {
                     cost_cents,
                 };
                 for update in loopback_event_to_updates(event) {
-                    #[cfg(feature = "unstable-message-id")]
-                    let update = apply_message_id_to_chunk(update, turn_mid.as_deref());
-                    #[cfg(not(feature = "unstable-message-id"))]
-                    let update = update;
                     let notification =
                         acp::schema::SessionNotification::new(session_id.clone(), update);
                     if let Err(e) = self.send_notification(session_id, notification).await {
@@ -2638,10 +2518,6 @@ impl ZephAcpAgentState {
                         }
                     });
                 }
-                #[cfg(feature = "unstable-message-id")]
-                let update = apply_message_id_to_chunk(update, turn_mid.as_deref());
-                #[cfg(not(feature = "unstable-message-id"))]
-                let update = update;
                 let notification =
                     acp::schema::SessionNotification::new(session_id.clone(), update);
                 if let Err(e) = self.send_notification(session_id, notification).await {
@@ -2845,8 +2721,6 @@ impl ZephAcpAgentState {
             thinking_enabled: AtomicBool::new(false),
             auto_approve_level: Mutex::new("suggest".to_owned()),
             shell_executor,
-            #[cfg(feature = "unstable-message-id")]
-            current_message_id: std::sync::Mutex::new(None),
             #[cfg(feature = "unstable-elicitation")]
             elicitation_bridge_handle: None,
             #[cfg(feature = "unstable-session-usage")]
@@ -3017,7 +2891,7 @@ impl ZephAcpAgentState {
                 Ok(Some(acp::schema::ExtResponse::new(raw.into())))
             }
             "providers/set" => {
-                let req: schema::SetProvidersRequest = serde_json::from_str(args.params.get())
+                let req: schema::SetProviderRequest = serde_json::from_str(args.params.get())
                     .map_err(|e| acp::Error::invalid_request().data(e.to_string()))?;
                 let resp = self.do_set_providers(req)?;
                 let json = serde_json::to_string(&resp)
@@ -3027,8 +2901,9 @@ impl ZephAcpAgentState {
                 Ok(Some(acp::schema::ExtResponse::new(raw.into())))
             }
             "providers/disable" => {
-                let req: schema::DisableProvidersRequest = serde_json::from_str(args.params.get())
-                    .map_err(|e| acp::Error::invalid_request().data(e.to_string()))?;
+                let req: schema::DisableProviderRequest =
+                    serde_json::from_str(args.params.get())
+                        .map_err(|e| acp::Error::invalid_request().data(e.to_string()))?;
                 let resp = self.do_disable_providers(req)?;
                 let json = serde_json::to_string(&resp)
                     .map_err(|e| acp::Error::internal_error().data(e.to_string()))?;
@@ -3097,8 +2972,8 @@ impl ZephAcpAgentState {
     #[tracing::instrument(skip_all, name = "acp.handler.set_providers")]
     pub(crate) fn do_set_providers(
         &self,
-        req: agent_client_protocol_schema::SetProvidersRequest,
-    ) -> acp::Result<agent_client_protocol_schema::SetProvidersResponse> {
+        req: agent_client_protocol_schema::SetProviderRequest,
+    ) -> acp::Result<agent_client_protocol_schema::SetProviderResponse> {
         if !self.provider_names.iter().any(|(name, _)| name == &req.id) {
             return Err(
                 acp::Error::invalid_params().data(format!("unknown provider id: {}", req.id))
@@ -3113,7 +2988,7 @@ impl ZephAcpAgentState {
             },
         );
         tracing::debug!(provider_id = %req.id, "provider override set");
-        Ok(agent_client_protocol_schema::SetProvidersResponse::new())
+        Ok(agent_client_protocol_schema::SetProviderResponse::new())
     }
 
     /// Handle `providers/disable` — mark a provider as disabled for this connection.
@@ -3122,17 +2997,17 @@ impl ZephAcpAgentState {
     ///
     /// # Errors
     ///
-    /// Always succeeds; returns `DisableProvidersResponse`.
+    /// Always succeeds; returns `DisableProviderResponse`.
     #[cfg(feature = "unstable-llm-providers")]
     #[tracing::instrument(skip_all, name = "acp.handler.disable_providers")]
     pub(crate) fn do_disable_providers(
         &self,
-        req: agent_client_protocol_schema::DisableProvidersRequest,
-    ) -> acp::Result<agent_client_protocol_schema::DisableProvidersResponse> {
+        req: agent_client_protocol_schema::DisableProviderRequest,
+    ) -> acp::Result<agent_client_protocol_schema::DisableProviderResponse> {
         let id = req.id;
         tracing::debug!(provider_id = %id, "provider disabled");
         self.global_disabled_providers.lock().insert(id);
-        Ok(agent_client_protocol_schema::DisableProvidersResponse::new())
+        Ok(agent_client_protocol_schema::DisableProviderResponse::new())
     }
 }
 
@@ -3163,20 +3038,13 @@ fn compute_stop_reason(cancelled: bool, stop_hint: Option<StopHint>) -> acp::sch
     }
 }
 
-/// Construct the `PromptResponse`, optionally echoing `turn_message_id` and attaching
-/// per-turn token usage when the `unstable-session-usage` feature is enabled.
+/// Construct the `PromptResponse`, attaching per-turn token usage when the
+/// `unstable-session-usage` feature is enabled.
 fn build_prompt_response(
-    #[cfg(feature = "unstable-message-id")] turn_message_id: Option<&str>,
     stop_reason: acp::schema::StopReason,
     #[cfg(feature = "unstable-session-usage")] turn_usage: TurnUsage,
 ) -> acp::schema::PromptResponse {
     let r = acp::schema::PromptResponse::new(stop_reason);
-    #[cfg(feature = "unstable-message-id")]
-    let r = if let Some(mid) = turn_message_id {
-        r.user_message_id(mid.to_owned())
-    } else {
-        r
-    };
     #[cfg(feature = "unstable-session-usage")]
     let r = {
         let total = turn_usage
@@ -3269,21 +3137,12 @@ pub async fn run_agent(
     state: Arc<ZephAcpAgentState>,
     transport: impl acp::ConnectTo<acp::Agent>,
 ) -> acp::Result<()> {
-    #[cfg(feature = "unstable-session-delete")]
-    use handlers::close_session;
-    #[cfg(feature = "unstable-session-delete")]
-    use handlers::delete_session;
     #[cfg(feature = "unstable-session-fork")]
     use handlers::fork_session;
-    #[cfg(feature = "unstable-logout")]
-    use handlers::logout;
-    #[cfg(feature = "unstable-session-resume")]
-    use handlers::resume_session;
-    #[cfg(feature = "unstable-session-model")]
-    use handlers::set_session_model;
     use handlers::{
-        authenticate, cancel, dispatch, initialize, list_sessions, load_session, new_session,
-        prompt, set_session_config_option, set_session_mode,
+        authenticate, cancel, close_session, delete_session, dispatch, initialize, list_sessions,
+        load_session, logout, new_session, prompt, resume_session, set_session_config_option,
+        set_session_mode,
     };
 
     let builder = acp::Agent
@@ -3328,12 +3187,10 @@ pub async fn run_agent(
             acp::on_receive_notification!(),
         );
 
-    #[cfg(feature = "unstable-session-delete")]
     let builder = builder.on_receive_request(
         req_handler!(state, close_session::handle_close_session),
         acp::on_receive_request!(),
     );
-    #[cfg(feature = "unstable-session-delete")]
     let builder = builder.on_receive_request(
         req_handler!(state, delete_session::handle_delete_session),
         acp::on_receive_request!(),
@@ -3343,17 +3200,10 @@ pub async fn run_agent(
         req_handler!(state, fork_session::handle_fork_session),
         acp::on_receive_request!(),
     );
-    #[cfg(feature = "unstable-session-resume")]
     let builder = builder.on_receive_request(
         req_handler!(state, resume_session::handle_resume_session),
         acp::on_receive_request!(),
     );
-    #[cfg(feature = "unstable-session-model")]
-    let builder = builder.on_receive_request(
-        req_handler!(state, set_session_model::handle_set_session_model),
-        acp::on_receive_request!(),
-    );
-    #[cfg(feature = "unstable-logout")]
     let builder = builder.on_receive_request(
         req_handler!(state, logout::handle_logout),
         acp::on_receive_request!(),
@@ -3374,30 +3224,6 @@ pub async fn run_agent(
         .await
 }
 
-/// Attach `message_id` to `AgentMessageChunk`, `UserMessageChunk`, and `AgentThoughtChunk`
-/// updates when a message id is present for this turn.
-#[cfg(feature = "unstable-message-id")]
-fn apply_message_id_to_chunk(
-    update: acp::schema::SessionUpdate,
-    message_id: Option<&str>,
-) -> acp::schema::SessionUpdate {
-    let Some(mid) = message_id else {
-        return update;
-    };
-    match update {
-        acp::schema::SessionUpdate::AgentMessageChunk(chunk) => {
-            acp::schema::SessionUpdate::AgentMessageChunk(chunk.message_id(mid.to_owned()))
-        }
-        acp::schema::SessionUpdate::UserMessageChunk(chunk) => {
-            acp::schema::SessionUpdate::UserMessageChunk(chunk.message_id(mid.to_owned()))
-        }
-        acp::schema::SessionUpdate::AgentThoughtChunk(chunk) => {
-            acp::schema::SessionUpdate::AgentThoughtChunk(chunk.message_id(mid.to_owned()))
-        }
-        other => other,
-    }
-}
-
 /// Compile-time assertions that ACP state and executors are `Send + Sync`.
 const _: () = {
     #[allow(clippy::used_underscore_items)]
@@ -3481,7 +3307,7 @@ mod providers_tests {
     fn disable_provider_hides_current_config_in_list() {
         let state = make_state();
         state
-            .do_disable_providers(schema::DisableProvidersRequest::new("openai"))
+            .do_disable_providers(schema::DisableProviderRequest::new("openai"))
             .unwrap();
         let resp = state
             .do_list_providers(schema::ListProvidersRequest::new())
@@ -3502,7 +3328,7 @@ mod providers_tests {
     fn disable_unknown_provider_succeeds() {
         let state = make_state();
         state
-            .do_disable_providers(schema::DisableProvidersRequest::new("nonexistent"))
+            .do_disable_providers(schema::DisableProviderRequest::new("nonexistent"))
             .unwrap();
     }
 
@@ -3511,7 +3337,7 @@ mod providers_tests {
         let state = make_state();
         let err = state
             .do_set_providers(
-                schema::SetProvidersRequest::new(
+                schema::SetProviderRequest::new(
                     "unknown_provider",
                     schema::LlmProtocol::OpenAi,
                     "https://evil.example.com",
@@ -3531,7 +3357,7 @@ mod providers_tests {
         let state = make_state();
         state
             .do_set_providers(
-                schema::SetProvidersRequest::new(
+                schema::SetProviderRequest::new(
                     "openai",
                     schema::LlmProtocol::OpenAi,
                     "https://custom.example.com",
@@ -3552,7 +3378,7 @@ mod providers_tests {
         let state = make_state();
         state
             .do_set_providers(
-                schema::SetProvidersRequest::new(
+                schema::SetProviderRequest::new(
                     "openai",
                     schema::LlmProtocol::OpenAi,
                     "https://custom.example.com",
@@ -3561,7 +3387,7 @@ mod providers_tests {
             )
             .unwrap();
         state
-            .do_disable_providers(schema::DisableProvidersRequest::new("openai"))
+            .do_disable_providers(schema::DisableProviderRequest::new("openai"))
             .unwrap();
         let resp = state
             .do_list_providers(schema::ListProvidersRequest::new())
@@ -3574,56 +3400,6 @@ mod providers_tests {
     }
 }
 
-#[cfg(all(test, feature = "unstable-message-id"))]
-mod message_id_tests {
-    use super::*;
-
-    fn agent_chunk(text: &str) -> acp::schema::SessionUpdate {
-        acp::schema::SessionUpdate::AgentMessageChunk(acp::schema::ContentChunk::new(
-            text.to_owned().into(),
-        ))
-    }
-
-    fn user_chunk(text: &str) -> acp::schema::SessionUpdate {
-        acp::schema::SessionUpdate::UserMessageChunk(acp::schema::ContentChunk::new(
-            text.to_owned().into(),
-        ))
-    }
-
-    #[test]
-    fn apply_sets_message_id_on_agent_chunk() {
-        let update = agent_chunk("hello");
-        let result = apply_message_id_to_chunk(update, Some("msg-001"));
-        if let acp::schema::SessionUpdate::AgentMessageChunk(chunk) = result {
-            assert_eq!(chunk.message_id, Some("msg-001".to_owned()));
-        } else {
-            panic!("expected AgentMessageChunk");
-        }
-    }
-
-    #[test]
-    fn apply_sets_message_id_on_user_chunk() {
-        let update = user_chunk("hi");
-        let result = apply_message_id_to_chunk(update, Some("msg-002"));
-        if let acp::schema::SessionUpdate::UserMessageChunk(chunk) = result {
-            assert_eq!(chunk.message_id, Some("msg-002".to_owned()));
-        } else {
-            panic!("expected UserMessageChunk");
-        }
-    }
-
-    #[test]
-    fn apply_none_message_id_is_noop() {
-        let update = agent_chunk("hello");
-        let result = apply_message_id_to_chunk(update, None);
-        if let acp::schema::SessionUpdate::AgentMessageChunk(chunk) = result {
-            assert_eq!(chunk.message_id, None);
-        } else {
-            panic!("expected AgentMessageChunk");
-        }
-    }
-}
-
 #[cfg(all(test, feature = "unstable-session-usage"))]
 mod usage_tests {
     use super::*;
@@ -3657,12 +3433,7 @@ mod usage_tests {
             cache_read_tokens: 10,
             cache_write_tokens: 0,
         };
-        let resp = build_prompt_response(
-            #[cfg(feature = "unstable-message-id")]
-            None,
-            acp::schema::StopReason::EndTurn,
-            turn_usage,
-        );
+        let resp = build_prompt_response(acp::schema::StopReason::EndTurn, turn_usage);
         let u = resp.usage.expect("usage should be set");
         assert_eq!(u.total_tokens, 150);
         assert_eq!(u.input_tokens, 100);
@@ -3678,12 +3449,7 @@ mod usage_tests {
     #[test]
     fn build_prompt_response_zero_usage_still_attaches() {
         let turn_usage = TurnUsage::default();
-        let resp = build_prompt_response(
-            #[cfg(feature = "unstable-message-id")]
-            None,
-            acp::schema::StopReason::EndTurn,
-            turn_usage,
-        );
+        let resp = build_prompt_response(acp::schema::StopReason::EndTurn, turn_usage);
         let u = resp
             .usage
             .expect("usage should be set even for zero tokens");
diff --git a/crates/zeph-acp/src/agent/tests.rs b/crates/zeph-acp/src/agent/tests.rs
index f6ee1be79..ecae9efd3 100644
--- a/crates/zeph-acp/src/agent/tests.rs
+++ b/crates/zeph-acp/src/agent/tests.rs
@@ -1468,7 +1468,6 @@ async fn initialize_advertises_session_capabilities() {
                 session_caps.resume.is_some(),
                 "resume capability must be advertised"
             );
-            #[cfg(feature = "unstable-session-delete")]
             assert!(
                 session_caps.close.is_some(),
                 "close capability must be advertised"
@@ -1961,7 +1960,6 @@ async fn fork_session_creates_new_session_from_existing() {
         .await;
 }
 
-#[cfg(feature = "unstable-session-resume")]
 #[tokio::test]
 async fn resume_session_returns_ok_for_active() {
     let local = tokio::task::LocalSet::new();
@@ -1983,7 +1981,6 @@ async fn resume_session_returns_ok_for_active() {
         .await;
 }
 
-#[cfg(feature = "unstable-session-resume")]
 #[tokio::test]
 async fn resume_session_errors_for_unknown() {
     let local = tokio::task::LocalSet::new();
@@ -2334,62 +2331,6 @@ fn loopback_tool_output_multiline_preserves_newlines_in_terminal_data() {
     }
 }
 
-// --- #958 SetSessionModel ---
-
-#[cfg(feature = "unstable-session-model")]
-#[tokio::test]
-async fn set_session_model_no_factory_errors() {
-    let local = tokio::task::LocalSet::new();
-    local
-        .run_until(async {
-            let (agent, mut rx) = make_agent();
-            let resp = agent
-                .new_session(acp::NewSessionRequest::new(std::path::PathBuf::from(".")))
-                .await
-                .unwrap();
-            while let Ok((_, ack)) = rx.try_recv() {
-                let _ = ack.send(());
-            }
-            let result = agent
-                .set_session_model(acp::SetSessionModelRequest::new(
-                    resp.session_id,
-                    "some:model",
-                ))
-                .await;
-            assert!(result.is_err());
-        })
-        .await;
-}
-
-#[cfg(feature = "unstable-session-model")]
-#[tokio::test]
-async fn set_session_model_rejects_unknown_model() {
-    let local = tokio::task::LocalSet::new();
-    local
-        .run_until(async {
-            let (tx, _rx) = tokio::sync::mpsc::unbounded_channel();
-            let conn_slot = std::rc::Rc::new(std::cell::RefCell::new(None));
-            let factory: ProviderFactory = Arc::new(|_| None);
-            let agent = ZephAcpAgent::new(make_spawner(), tx, conn_slot, 4, 1800, None)
-                .with_provider_factory(
-                    factory,
-                    shared_models(vec!["claude:claude-sonnet-4-6".to_owned()]),
-                );
-            let resp = agent
-                .new_session(acp::NewSessionRequest::new(std::path::PathBuf::from(".")))
-                .await
-                .unwrap();
-            let result = agent
-                .set_session_model(acp::SetSessionModelRequest::new(
-                    resp.session_id,
-                    "ollama:llama3",
-                ))
-                .await;
-            assert!(result.is_err());
-        })
-        .await;
-}
-
 #[tokio::test]
 async fn new_session_meta_contains_project_rules() {
     let local = tokio::task::LocalSet::new();
@@ -3789,7 +3730,6 @@ async fn non_llm_slash_commands_all_complete_without_hanging() {
         .await;
 }
 
-#[cfg(feature = "unstable-session-delete")]
 #[tokio::test]
 async fn close_session_removes_entry() {
     let local = tokio::task::LocalSet::new();
@@ -3819,7 +3759,6 @@ async fn close_session_removes_entry() {
         .await;
 }
 
-#[cfg(feature = "unstable-session-delete")]
 #[tokio::test]
 async fn close_session_unknown_id_is_ok() {
     let local = tokio::task::LocalSet::new();
@@ -3948,7 +3887,6 @@ async fn set_config_option_model_emits_session_info_update() {
         .await;
 }
 
-#[cfg(feature = "unstable-session-delete")]
 #[tokio::test]
 async fn close_session_signals_cancel() {
     let local = tokio::task::LocalSet::new();
diff --git a/crates/zeph-acp/src/lib.rs b/crates/zeph-acp/src/lib.rs
index b4e81a602..05edb8c09 100644
--- a/crates/zeph-acp/src/lib.rs
+++ b/crates/zeph-acp/src/lib.rs
@@ -38,7 +38,6 @@
 //! | `unstable-session-fork` | ACP session fork extension |
 //! | `unstable-session-resume` | ACP session resume (stable since acp 0.12.1; no SDK gate needed) |
 //! | `unstable-session-usage` | ACP session token-usage extension |
-//! | `unstable-session-model` | ACP session model-switching extension |
 //! | `unstable-elicitation` | ACP elicitation schema types |
 //! | `unstable-logout` | ACP logout extension |
 //!
diff --git a/crates/zeph-acp/src/transport/mod.rs b/crates/zeph-acp/src/transport/mod.rs
index ee816e9f1..4188485e2 100644
--- a/crates/zeph-acp/src/transport/mod.rs
+++ b/crates/zeph-acp/src/transport/mod.rs
@@ -122,7 +122,7 @@ pub struct AcpServerConfig {
     pub additional_directories: Vec<zeph_core::config::AdditionalDir>,
     /// Auth methods to advertise in the `initialize` response.
     pub auth_methods: Vec<zeph_core::config::AcpAuthMethod>,
-    /// When `true`, echo `PromptRequest.message_id` through responses and chunks.
+    /// Retained for config compatibility. `PromptRequest.message_id` was removed in acp 0.14.0.
     pub message_ids_enabled: bool,
     /// Per-request timeout configuration for elicitation, terminal, and MCP operations.
     pub timeouts: zeph_config::AcpTimeoutsConfig,
diff --git a/crates/zeph-acp/src/transport/stdio.rs b/crates/zeph-acp/src/transport/stdio.rs
index dfac024e1..e0a420d22 100644
--- a/crates/zeph-acp/src/transport/stdio.rs
+++ b/crates/zeph-acp/src/transport/stdio.rs
@@ -106,7 +106,6 @@ pub(crate) async fn build_agent_state(
     if !server_config.auth_methods.is_empty() {
         agent = agent.with_auth_methods(server_config.auth_methods);
     }
-    agent = agent.with_message_ids_enabled(server_config.message_ids_enabled);
     agent = agent.with_timeouts(server_config.timeouts);
 
     let state = Arc::new(agent);
diff --git a/specs/013-acp/spec.md b/specs/013-acp/spec.md
index 662239822..819548545 100644
--- a/specs/013-acp/spec.md
+++ b/specs/013-acp/spec.md
@@ -8,7 +8,7 @@ tags:
   - protocol
   - acp
 created: 2026-04-08
-updated: 2026-05-19
+updated: 2026-06-06
 status: approved
 related:
   - "[[MOC-specs]]"
@@ -19,7 +19,7 @@ related:
 
 > [!info]
 > ACP transports, session management, permissions, fork/resume,
-> capability advertisement, agent-client-protocol 0.12.1 / schema 0.13.2 compatibility.
+> capability advertisement, agent-client-protocol 0.14.0 / schema =0.13.6 compatibility.
 
 ## Spec Changelog
 
@@ -28,6 +28,7 @@ related:
 | 1.0 | 2026-04-08 | sdd | Initial spec (SDK 0.11.1 / schema 0.12.0) |
 | 1.1 | 2026-05-19 | sdd | Updated to SDK 0.12.1 / schema 0.13.2; added Providers API, Elicitation, MCP-over-ACP, Session Usage, Session Delete migration, v2 tracking, breaking changes resolution |
 | 1.2 | 2026-05-29 | sdd | Mark Providers API, Elicitation protocol, Session Usage, and session/delete as implemented; update SDK to 0.12.1; wire IDE-provided MCP servers into do_new_session; add blocking-await timeout note |
+| 1.3 | 2026-06-06 | sdd | ACP 0.14.0 protocol bump: bumped core 0.12.1→0.14.0, schema pinned =0.13.6; removed session/set_model RPC (model switching preserved via set_config_option); removed inbound message-id echo feature; renamed provider ext-method types to singular; stabilized delete/logout/resume/add-dirs feature flags; renamed session-usage upstream gate; added elicitation core passthrough; documented MessageId newtype change |
 
 ---
 
@@ -81,21 +82,22 @@ AcpSessionManager
 - Session fork: create a new session branching from an existing session at a given turn
 - Session resume: reconnect to an existing session by ID
 
-### Agent Spawner Contract (0.12.1)
+### Agent Spawner Contract (0.14.0)
 
-Agent sessions use the `Agent.builder()` / `run_agent()` pattern from
-`agent-client-protocol 0.11.1`, preserved in 0.12.1. Session state is `Arc`-wrapped.
+Agent sessions use the `Agent.builder()` / `run_agent()` pattern. Session state is `Arc`-wrapped.
 Session tasks are launched via `tokio::task::spawn_local` inside a `LocalSet` — the
 `AgentSpawner` closure returns `Pin<Box<dyn Future<Output = ()> + 'static>>` (`!Send`).
 
-SDK 0.12.0 removed `McpAcpTransport` and the direct `tokio` re-export. Zeph is unaffected:
-`McpAcpTransport` was never used, and Zeph has its own `tokio` dependency.
+SDK 0.12.0 removed `McpAcpTransport` and the direct `tokio` re-export; the dead
+`agent-client-protocol-tokio` crate was also removed entirely in the 0.14.0 bump.
+Zeph is unaffected: `McpAcpTransport` was never used, Zeph has its own `tokio` dependency,
+and `agent-client-protocol-tokio` was removed from both workspace `Cargo.toml` and `crates/zeph-acp/Cargo.toml`.
 
-`session/close` and `session/resume` were stabilized in SDK 0.12.0 (schema 0.12.2).
-The `unstable-session-resume` and `unstable-session-close` feature flags in Zeph should be
-removed after SDK upgrade to 0.12.1.
+`session/close`, `session/resume`, `session/delete`, and `session/logout` are unconditional in
+core 0.14.0. The corresponding `unstable-session-*` Zeph feature flags are tombstoned as
+no-op `= []` (retained only so root `Cargo.toml` forwarding resolves without changes).
 
-**Status: implemented** (SDK upgraded to 0.12.1 in commit #4464; `unstable-session-resume` and `unstable-session-close` feature flags removed)
+**Status: implemented** (SDK upgraded to 0.14.0 / schema =0.13.6)
 
 ## Permission Model
 
@@ -114,7 +116,7 @@ AcpPermissionGate (TOML-backed, SQLite-persisted)
 ## Protocol Messages
 
 - Rich content: images, file resources, binary data
-- Model switching: client can request a specific model per session
+- Model switching: client requests a specific model via `session/set_config_option` with `config_id="model"` (see Model Switching below)
 - Terminal forwarding: tool output streams back to IDE terminal
 - File tools: read/write/list within session working directory
 - MCP passthrough: MCP tools are forwarded to ACP client via `mcp_passthrough` capability
@@ -129,9 +131,13 @@ are available in PR4+:
 | `enabled` | bool | `false` | Enable ACP server |
 | `agent_name` | String | `"zeph"` | Agent name advertised to clients |
 | `transport` | String | `"stdio"` | Transport: `stdio`, `http`, `ws`, `both` |
-| `additional_directories` | `Vec<String>` | `[]` | **Request-side allowlist.** Paths a client may pass in `sessionInit.additionalDirectories`. Paths not in this list are rejected at session start. This is NOT a protocol advertisement — it is a server-side gate. |
+| `additional_directories` | `Vec<String>` | `[]` | **Request-side allowlist.** Paths a client may pass in `sessionInit.additionalDirectories`. Paths not in this list are rejected at session start. This is NOT a protocol advertisement — it is a server-side gate. Field is unconditional (degated in 0.14.0 bump). |
 | `auth_methods` | `Vec<String>` | `["agent"]` | Accepted authentication methods. MVP: only `"agent"` is valid. Unknown values are rejected at deserialization. |
-| `message_ids_enabled` | bool | `true` | Echo client-supplied `message_id` in `PromptResponse.user_message_id` and all streamed chunks. |
+
+> **Changed in 0.14.0 bump**: `message_ids_enabled` is retained as a no-op field for config-schema
+> compatibility (read by `acp_commands.rs`). The `PromptRequest.message_id` and
+> `PromptResponse.user_message_id` protocol fields were deleted upstream in schema 0.13.6; the
+> inbound message-id echo behaviour is removed.
 
 ### Key Invariants
 
@@ -140,8 +146,6 @@ are available in PR4+:
   `AcpError::PermissionDenied` at session start — never silently ignored
 - `auth_methods` must only contain `"agent"` for MVP; unknown variants cause a hard deserialization
   error at startup to prevent misconfigured deployments from silently accepting unexpected auth
-- When `message_ids_enabled = true`, every `PromptResponse` and every streamed chunk must carry the
-  originating `message_id` — partial echo (response but not chunks, or vice versa) is a bug
 
 ## Session CRUD Endpoints (#3902, #4252)
 
@@ -183,7 +187,7 @@ error    — session terminated due to an unhandled error
 
 ### session/close
 
-**Status: stable** (stabilized in schema 0.12.2, SDK 0.12.0)
+**Status: stable** (stabilized in schema 0.12.2, SDK 0.12.0; unconditional in core 0.14.0)
 
 `session/close` handler gracefully terminates an ACP session: flushes pending memory writes,
 cancels in-flight tool calls, persists session state to SQLite, and removes the session from
@@ -200,13 +204,29 @@ string for diagnostics (e.g., `"user_initiated"`, `"timeout"`, `"error"`).
 
 ### session/resume
 
-**Status: stable** (stabilized in schema 0.12.2, SDK 0.12.0)
+**Status: stable** (stabilized in schema 0.12.2, SDK 0.12.0; unconditional in core 0.14.0)
 
 Reconnect to an existing session by ID, restoring conversation history and tool context.
 Previously gated behind `unstable-session-resume` feature flag in Zeph.
 
-**Action required on SDK upgrade**: remove `unstable-session-resume` feature flag from
-`crates/zeph-acp/Cargo.toml` and root `Cargo.toml`. Use the stable API directly.
+The `unstable-session-resume` Zeph feature flag is now a tombstone `= []`. All `#[cfg(feature =
+"unstable-session-resume")]` gates are removed; the resume handler runs unconditionally.
+
+### session/delete
+
+**Status: stable** (unconditional in core 0.14.0)
+
+Remove a session from the `session/list` registry. Previously gated behind `unstable-session-delete`.
+The `unstable-session-delete` Zeph feature flag is now a tombstone `= []`. All cfg gates removed.
+
+Custom `_session/delete` extension (backward compat) is retained alongside the standard method.
+
+### session/logout
+
+**Status: stable** (unconditional in core 0.14.0)
+
+Previously gated behind `unstable-logout`. The `unstable-logout` Zeph feature flag is now a
+tombstone `= []`. All cfg gates removed; logout handler runs unconditionally.
 
 ### Capability Negotiation
 
@@ -219,11 +239,10 @@ ACP server advertises its capabilities in the `initialize` response and via the
 `GET /agent.json` returns a JSON document describing the agent's identity, declared capabilities, supported protocol version, and authentication methods. This endpoint is unauthenticated and used by IDE clients for discovery.
 
 ```json
-// after SDK upgrade to 0.12.1 / schema 0.13.2 (see I1)
 {
   "name": "...",
   "version": "...",
-  "protocol": "acp/0.13.2",
+  "protocol": "acp/0.13.6",
   "capabilities": ["tools", "memory", "streaming"],
   "authMethods": ["bearer"]
 }
@@ -231,8 +250,8 @@ ACP server advertises its capabilities in the `initialize` response and via the
 
 #### Protocol Version
 
-Zeph uses `agent-client-protocol 0.12.1` / `schema 0.13.2` (upgraded in commit #4464).
-The `/agent.json` `protocol` field reflects `"acp/0.13.2"` per the compiled crate version.
+Zeph uses `agent-client-protocol 0.14.0` / `schema =0.13.6`.
+The `/agent.json` `protocol` field reflects `"acp/0.13.6"` per the compiled schema crate version.
 
 #### Current Model in SessionInfoUpdate
 
@@ -257,13 +276,73 @@ exposing tools over ACP.
 
 ---
 
-## Unstable Features (feature: `acp-unstable`)
+## Feature Flags
+
+| Flag | Status | Notes |
+|------|--------|-------|
+| `unstable-session-fork` | **active** | Still gated upstream (`unstable_session_fork`) |
+| `unstable-session-usage` | **active** | Gate renamed upstream: now forwards `agent-client-protocol/unstable_end_turn_token_usage` (was `unstable_session_usage`). `Usage` struct + `PromptResponse.usage` field are ALL gated — not unconditional. |
+| `unstable-elicitation` | **active** | Now also adds `agent-client-protocol/unstable_elicitation` passthrough so core wires `elicitation/create` |
+| `unstable-llm-providers` | **active** | Still gated upstream (`unstable_llm_providers`); provider type renames apply here (see Providers API) |
+| `unstable-auth-methods` | **active** | Still gated upstream (`unstable_auth_methods`) |
+| `unstable-boolean-config` | **active** | Still gated upstream (`unstable_boolean_config`) |
+| `unstable-session-delete` | **tombstone** `= []` | Stabilized — `session/delete` handler is unconditional in core 0.14.0. Flag retained as no-op for workspace forwarding (root `Cargo.toml` references it). |
+| `unstable-session-resume` | **tombstone** `= []` | Stabilized — `session/resume` handler is unconditional in core 0.14.0. Flag retained as no-op. |
+| `unstable-logout` | **tombstone** `= []` | Stabilized — logout handler is unconditional in core 0.14.0. Flag retained as no-op. |
+| `unstable-session-add-dirs` | **tombstone** `= []` | Stabilized — `additional_directories` field is plain `Vec<PathBuf>`, unconditional in schema 0.13.6. Flag retained as no-op. |
+| `unstable-message-id` | **tombstone** `= []` | Removed — `PromptRequest.message_id` and `PromptResponse.user_message_id` deleted upstream. Entire inbound echo feature removed. Flag retained as no-op for workspace forwarding. |
+| `unstable-session-model` | **DELETED** | Removed entirely — `session/set_model` RPC deleted upstream. Feature name removed from Cargo.toml and root `Cargo.toml`. Model switching survives via `set_config_option`. |
+
+> **Tombstone flags** are `= []` no-ops retained solely so root `Cargo.toml` feature forwarding
+> resolves without changes. They add zero behavior.
+
+---
+
+## Model Switching
+
+**Status: preserved via stable mechanism**
+
+The dedicated `session/set_model` RPC method was removed upstream (deleted in `agent-client-protocol`
+0.14.0 / schema 0.13.6). This is NOT a capability loss.
+
+Model switching is FULLY preserved via two stable paths:
+
+1. **`session/set_config_option`** with `config_id="model"` and `value=<model-name>` — the
+   canonical stable path. Runs identical logic to the former `session/set_model`: calls
+   `provider_factory(value)`, validates against `available_models_snapshot()`, updates
+   `provider_override`, and emits `SessionInfoUpdate` with `model_meta`.
+2. **`$/model` slash command** — IDE/CLI convenience; internally dispatches to the same
+   `apply_session_config` path.
+
+`session/set_mode` (behavioral persona switch: `code`/`architect`/`ask`) is an orthogonal
+concept, NOT a replacement for model switching. Mode and model are independent.
+
+> **NEVER** describe the removal of `session/set_model` as a capability loss. Model switching
+> survives unconditionally via `session/set_config_option`.
+
+---
+
+## Message ID Echo (REMOVED)
+
+**Status: removed in 0.14.0 bump**
+
+`PromptRequest.message_id` and `PromptResponse.user_message_id` were deleted upstream in
+schema 0.13.6. The entire inbound message-id echo feature is removed from Zeph:
+
+- `message_ids_enabled` config field retained as no-op (config-schema compatibility)
+- `current_message_id` session slot removed
+- `build_prompt_response` no longer accepts or echoes a message ID
+- `apply_message_id_to_chunk` removed (no live data source)
+- `unstable-message-id` feature is a tombstone `= []`
+
+`ContentChunk.message_id` field still exists in schema 0.13.6 for potential future
+agent-generated per-chunk IDs, but Zeph does not inject it (no inbound source).
 
-- `unstable-session-list`: enumerate active sessions *(was already stable at 0.11.1)*
-- `unstable-session-fork`: fork session at a point
+### MessageId Type
 
-> **Note**: `unstable-session-resume` and `unstable-session-close` are no longer unstable
-> upstream (stabilized in schema 0.12.2). These flags should be removed after SDK upgrade to 0.12.1.
+In schema 0.13.6, `MessageId` is a newtype: `MessageId(pub Arc<str>)`. The chunk builder
+accepts `impl IntoOption<MessageId>`, where `IntoOption<MessageId>` is implemented for
+`&str` **only** (not `String`). Passing `String` will not compile — always pass `&str`.
 
 ---
 
@@ -281,6 +360,18 @@ Schema 0.11.7 introduced a providers management API (`unstable` in SDK):
 | `providers/set` | Sets the active provider for the session |
 | `providers/disable` | Disables a provider for the session |
 
+**Breaking change in 0.14.0 bump — type renames (singular):**
+
+| Old type name | New type name |
+|---------------|---------------|
+| `SetProvidersRequest` | `SetProviderRequest` |
+| `SetProvidersResponse` | `SetProviderResponse` |
+| `DisableProvidersRequest` | `DisableProviderRequest` |
+| `DisableProvidersResponse` | `DisableProviderResponse` |
+
+All renamed types have `::new()` constructors. All four remain gated behind
+`unstable_llm_providers` (Zeph flag `unstable-llm-providers` retained).
+
 **Design note — impedance mismatch**: The Providers API is NOT a direct mapping to Zeph's
 `[[llm.providers]]` TOML config. Key tensions:
 
@@ -319,11 +410,10 @@ Schema 0.11.5 introduced structured user input (elicitation) across three scopes
 - **Request scope** (0.11.5, PR #771): agent requests structured input during prompt processing
 - **Scoped by mode** (0.11.6, PR #966): elicitation behavior varies by mode
 
-**Current Zeph state**: `unstable-elicitation = []` in `crates/zeph-acp/Cargo.toml` is a
-**local empty feature flag** — it does NOT pass through to `agent-client-protocol/unstable_elicitation`.
-The SDK 0.11.1 has no corresponding feature flag. This means elicitation in Zeph is not
-SDK-gated; it requires a custom implementation or will need to align with SDK 0.12.x's
-elicitation support. This is NOT a simple "enable a feature flag" task.
+**Current Zeph state**: `unstable-elicitation` in `crates/zeph-acp/Cargo.toml` now includes
+`agent-client-protocol/unstable_elicitation` passthrough (added in the 0.14.0 bump). This wires
+core's `elicitation/create` request dispatch path. Zeph already implements elicitation in
+`elicitation.rs`; the core passthrough ensures `elicitation/create` is registered.
 
 **Fixed**: `elicitation_timeout_secs` is now read from `_meta` in `mcp_bridge.rs` (commit #4453).
 `elicitation_enabled` is read from `_meta` rather than being hardcoded to `false` (commit #4441).
@@ -424,9 +514,25 @@ without `_` prefix are rejected).
 | `McpAcpTransport` struct removed | Zeph does not use `McpAcpTransport` (grep confirmed) | **Resolved — no action** |
 | `McpConnectRequest.acp_url` renamed to `acp_id` | Zeph does not use `acp_url` (grep confirmed) | **Resolved — no action** |
 | `tokio` re-export removed from SDK | Zeph uses its own `tokio` dependency — does not import tokio types from the SDK (grep confirmed) | **Resolved — no action** |
-| `session/close` and `session/resume` stabilized | Zeph uses feature flags `unstable-session-close` and `unstable-session-resume` — remove after SDK upgrade | **Pending SDK upgrade** |
+| `session/close` and `session/resume` stabilized | Feature flags removed; handlers unconditional | **Resolved** |
 | `_` prefix required for extension methods | Zeph's custom extension is already `_session/delete` | **Resolved — compliant** |
 
+## Breaking Changes Resolution (SDK 0.12.1 → 0.14.0)
+
+| Breaking Change | Impact on Zeph | Status |
+|----------------|---------------|--------|
+| `agent-client-protocol` bumped to `0.14.0`, schema pinned `=0.13.6` | Workspace `Cargo.toml` updated; `=` pin required for schema | **Resolved** |
+| `agent-client-protocol-tokio` dead dep removed | Dep line deleted from workspace + crate `Cargo.toml` | **Resolved** |
+| `session/set_model` RPC deleted upstream | Handler + file + tests deleted; model switching preserved via `session/set_config_option` (config_id="model") | **Resolved** |
+| `PromptRequest.message_id` removed upstream | Entire inbound message-id echo feature removed; `unstable-message-id` tombstoned | **Resolved** |
+| `PromptResponse.user_message_id` removed upstream | Removed from `build_prompt_response`; was a hard compile break | **Resolved** |
+| `SetProvidersRequest/Response` → `SetProviderRequest/Response` (singular) | Renamed at all ext-method dispatch sites | **Resolved** |
+| `DisableProvidersRequest/Response` → `DisableProviderRequest/Response` (singular) | Renamed at all ext-method dispatch sites | **Resolved** |
+| `unstable_session_usage` gate renamed to `unstable_end_turn_token_usage` | `unstable-session-usage` feature re-pointed; `Usage` struct + `PromptResponse.usage` still gated | **Resolved** |
+| `unstable_elicitation` added to core 0.14.0 | `unstable-elicitation` feature now passes through to core | **Resolved** |
+| `MessageId` type changed to newtype `MessageId(pub Arc<str>)` | `IntoOption<MessageId>` impl for `&str` only — no `String` | **Resolved** |
+| `session/delete`, `session/resume`, `session/logout`, `additional_directories` stabilized | Feature flags tombstoned `= []`; all cfg gates removed | **Resolved** |
+
 ---
 
 ## Implementation Gap Tracker
@@ -442,10 +548,16 @@ without `_` prefix are rejected).
 | I7 | Session usage reporting | **Implemented** (#4522) | ✓ Done | — |
 | I8 | `elicitation_timeout_secs` hardcoded | **Fixed** — read from `_meta` (#4453) | ✓ Done | — |
 | I9 | Shell timeout hardcoded | 10+ sites in `terminal.rs` with 120s | `[acp.timeouts]` config section | P3 |
-| I10 | Logout method | `handlers/logout.rs` exists | Verify against upstream Preview RFD | P3 |
+| I10 | Logout method | **Stable** — degated in 0.14.0 bump | ✓ Done | — |
 | I11 | Agent telemetry export | Local tracing only | Follow upstream RFD (not yet in schema) | P4 |
 | I12 | IDE-provided MCP servers | **Implemented** — wired into `do_new_session` (#4444) | ✓ Done | — |
 | I13 | Blocking awaits in handlers | **Fixed** — bounded with configurable timeouts (#4538) | ✓ Done | — |
+| I14 | SDK upgrade 0.12.1 → 0.14.0 | **In progress** (this PR) | ✓ Done (pending merge) | — |
+| I15 | Remove `session/set_model` handler | **In progress** (this PR) | ✓ Done (pending merge) | — |
+| I16 | Remove inbound message-id echo | **In progress** (this PR) | ✓ Done (pending merge) | — |
+| I17 | Provider type renames (singular) | **In progress** (this PR) | ✓ Done (pending merge) | — |
+| I18 | Re-point `unstable-session-usage` gate | **In progress** (this PR) | ✓ Done (pending merge) | — |
+| I19 | Add elicitation core passthrough | **In progress** (this PR) | ✓ Done (pending merge) | — |
 
 ---
 
@@ -539,33 +651,34 @@ No action needed now. Monitor upstream v2 progress at https://github.com/agentcl
 
 ---
 
-## Addendum: Interop Protocol Gap Analysis (2026-04-17, updated 2026-05-19)
+## Addendum: Interop Protocol Gap Analysis (2026-04-17, updated 2026-06-06)
 
 Cross-reference: `specs/045-interop-protocol-gaps/spec.md`
 
 ### ACP Baseline vs. arXiv:2505.02279 Survey
 
-Zeph's ACP implementation is currently based on `agent-client-protocol = "0.11.1"` (workspace
-`Cargo.toml`). Current upstream: SDK **0.12.1** / schema **0.13.2** (2026-05-17).
+Zeph's ACP implementation is based on `agent-client-protocol = "0.14.0"` / schema `=0.13.6`
+(workspace `Cargo.toml`, updated in this PR).
 
 The survey (arXiv:2505.02279) describes ACP's capability advertisement and re-negotiation
 model as a differentiating feature vs. MCP and A2A.
 
-**Capability re-negotiation status: Unverified.** The `agent-client-protocol` 0.11 SDK
-includes capability fields in the session handshake message. Dynamic re-negotiation during
-an active session has not been confirmed tested in Zeph's `AcpSessionManager`.
+**Capability re-negotiation status: Unverified.** Dynamic re-negotiation during an active
+session has not been confirmed tested in Zeph's `AcpSessionManager`.
 
 This does not block any current feature. It is tracked as a P3 follow-up in
 `specs/045-interop-protocol-gaps/spec.md` under "P3 Follow-up: ACP capability re-negotiation
 integration test".
 
-### Version Upgrade Note
-
-To upgrade `agent-client-protocol` from 0.11.1 to 0.12.1:
-1. Review breaking changes in the SDK changelog (summarized in Breaking Changes Resolution table above).
-2. Update `Cargo.toml` workspace dependency: `agent-client-protocol = "0.12.1"`, `agent-client-protocol-tokio = "0.12.1"`.
-3. Remove `unstable-session-resume` and `unstable-session-close` feature flags from `crates/zeph-acp/Cargo.toml` and root `Cargo.toml`.
-4. Run `cargo nextest run --workspace --features full --lib --bins` — ACP session tests must pass.
-5. Verify no tokio type imports from `agent_client_protocol` or `agent_client_protocol_tokio`.
-6. Update the capability matrix in `specs/045-interop-protocol-gaps/spec.md` accordingly.
-7. Update `/agent.json` `protocol` field from `"acp/0.12.0"` to `"acp/0.13.2"`.
+### Version Upgrade Note (0.12.1 → 0.14.0, completed in this PR)
+
+1. Review Breaking Changes Resolution table (SDK 0.12.1 → 0.14.0) above.
+2. Workspace: `agent-client-protocol = "0.14.0"`, `agent-client-protocol-schema = "=0.13.6"`; delete `agent-client-protocol-tokio`.
+3. Crate `Cargo.toml`: tombstone degated features as `= []`; fix `unstable-session-usage` → `["agent-client-protocol/unstable_end_turn_token_usage"]`; add core passthrough to `unstable-elicitation`.
+4. Delete `handlers/set_session_model.rs`; remove all `session/set_model` handler code and tests.
+5. Remove all inbound message-id plumbing; `message_ids_enabled` config field retained as no-op.
+6. Rename `SetProvidersRequest/Response` and `DisableProvidersRequest/Response` to singular.
+7. Degate all cfg sites for delete/logout/resume/add-dirs.
+8. Build: `cargo check -p zeph-acp --features full`; `cargo nextest run -p zeph-acp --all-features`.
+9. Live round-trip test: session/new → prompt → set_config_option{model} → set_mode → session/delete → logout.
+10. Update `/agent.json` `protocol` field to `"acp/0.13.6"`.
diff --git a/specs/README.md b/specs/README.md
index f05c90b0a..7b6519141 100644
--- a/specs/README.md
+++ b/specs/README.md
@@ -95,7 +95,7 @@ Spec IDs (001–065) follow a logical grouping:
 | `011-tui/spec.md` | ratatui dashboard, spinner rule for background operations, TuiChannel, RenderCache, embed backfill progress, multi-session `SessionRegistry`, `/session` commands, compact paste indicator; Fleet panel (`f` key, #3884); reasoning token tracking; terminal title (#4354); fleet session lifecycle wiring (#4363) | `zeph-tui` |
 | `012-graph-memory/spec.md` | Entity graph, BFS recall, community detection, MAGMA typed edges, SYNAPSE spreading activation | `zeph-memory` |
 | `004-memory/004-6-graph-memory.md` | Graph memory sub-spec (concise reference within 004-memory): MAGMA typed edges, SYNAPSE config, A-MEM link weights, key invariants | `zeph-memory` |
-| `013-acp/spec.md` | ACP transports, session management, permissions, fork/resume, session/close handlers, capability advertisement, /agent.json endpoint | `zeph-acp` |
+| `013-acp/spec.md` | ACP transports, session management, permissions, fork/resume, session/close handlers, capability advertisement, /agent.json endpoint; 0.14.0 bump: session/set_model removed, message-id echo removed, provider renames, feature flag stabilizations | `zeph-acp` |
 | `014-a2a/spec.md` | A2A protocol, agent discovery, JSON-RPC 2.0, IBCT (Invocation-Bound Capability Tokens), HMAC-SHA256 signatures | `zeph-a2a` |
 | `015-self-learning/spec.md` | FeedbackDetector (multi-language), Wilson score, trust model, SAGE RL cross-session reward, ARISE trace improvement, STEM pattern-to-skill migration, ERL experiential learning | `zeph-skills` |
 | `016-agent-feedback/spec.md` | Implicit correction detection: `FeedbackDetector` (regex-only, 7 languages, dual anchoring tiers), `JudgeDetector` (LLM judge with adaptive thresholds, sliding-window rate limiter 5/min), four correction kinds (explicit rejection, alternative request, repetition, self-correction), CJK limitations | `zeph-agent-feedback` |