fix(agent-mode): stop cancelled OpenCode retries

src/agentMode/backends/opencode/OpencodeBackend.ts

@@ -317,9 +317,9 @@ export async function buildOpencodeConfig(
   // native `build` agent this only adds the external_directory key — bash/edit
   // stay at opencode's permissive defaults, so it does not start asking.
   //
-  // NOTE (version-sensitive, pinned opencode 1.15.13): the `external_directory`
+  // NOTE (version-sensitive, pinned opencode 1.16.0): the `external_directory`
   // permission key and the `{ "<glob>": "allow" }` shape are confirmed against
-  // 1.15.13; re-verify when the pinned opencode version changes.
+  // 1.16.0; re-verify when the pinned opencode version changes.
   const externalDirectoryPermission = cacheRoot
     ? { external_directory: { [`${cacheRoot}/**`]: "allow" } }
     : undefined;

src/agentMode/backends/opencode/OpencodeBinaryManager.test.ts

@@ -56,6 +56,7 @@ import * as os from "node:os";
 import * as path from "node:path";
 import {
   computeInstallState,
+  isOpencodeVersionOutdated,
   legacyVaultDataDir,
   opencodeManagedDataDir,
   OpencodeBinaryManager,
@@ -65,6 +66,13 @@ import {
   verifyOpencodeBinary,
 } from "./OpencodeBinaryManager";
 
+describe("isOpencodeVersionOutdated", () => {
+  it("requires the ACP cancellation fix shipped in 1.16.0", () => {
+    expect(isOpencodeVersionOutdated("1.15.13")).toBe(true);
+    expect(isOpencodeVersionOutdated("1.16.0")).toBe(false);
+  });
+});
+
 // Pull the mock helpers off the mocked module without TS complaints.
 const settingsMock = jest.requireMock("@/settings/model");
 

src/agentMode/backends/opencode/OpencodeBinaryManager.ts

@@ -128,10 +128,10 @@ export function readOpencodeSettings(): OpencodeBackendSettings {
 
 /**
  * Whether an installed opencode version predates the minimum the plugin
- * supports ({@link OPENCODE_MIN_ACP_VERSION}). Older binaries advertise models
- * through the now-removed ACP `models` state, so the picker can't surface them.
- * An unknown version isn't flagged — we can't prove it's old, and a missing
- * install is handled by the install prompt instead.
+ * supports ({@link OPENCODE_MIN_ACP_VERSION}). Older binaries either predate
+ * the current model catalog or leave the backing turn running after ACP
+ * cancellation. An unknown version isn't flagged — we can't prove it's old,
+ * and a missing install is handled by the install prompt instead.
  */
 export function isOpencodeVersionOutdated(version: string | undefined): boolean {
   if (!version) return false;

src/agentMode/session/AgentSession.test.ts

@@ -1029,6 +1029,97 @@ describe("AgentSession.sendPrompt", () => {
     resolvePrompt!({ stopReason: "cancelled" });
     expect(await turn).toBe("cancelled");
   });
+
+  it("settles locally and drops retry output when backend cancellation fails", async () => {
+    const mock = makeMockBackend();
+    let resolveBackingPrompt: ((value: { stopReason: "cancelled" }) => void) | null = null;
+    let resolveSecondPrompt: ((value: { stopReason: "end_turn" }) => void) | null = null;
+    mock.prompt
+      .mockImplementationOnce(
+        () =>
+          new Promise((resolve) => {
+            resolveBackingPrompt = resolve;
+          })
+      )
+      .mockImplementationOnce(
+        () =>
+          new Promise((resolve) => {
+            resolveSecondPrompt = resolve;
+          })
+      );
+    const session = new AgentSession({
+      backend: mock.asBackend,
+      backendSessionId: "acp-1",
+      internalId: "internal-1",
+      backendId: "opencode",
+    });
+    const emitChunk = (
+      sessionUpdate: "agent_thought_chunk" | "agent_message_chunk",
+      text: string,
+      messageId = "msg-first"
+    ) =>
+      mock.emit({
+        sessionId: "acp-1",
+        update: { sessionUpdate, messageId, content: { type: "text", text } },
+      });
+    const { turn } = session.sendPrompt("first");
+
+    emitChunk("agent_thought_chunk", "initial thought");
+    emitChunk("agent_message_chunk", "partial answer");
+    mock.cancel.mockImplementation(() => {
+      emitChunk("agent_thought_chunk", " retry during cancel");
+      mock.emit({
+        sessionId: "acp-1",
+        update: {
+          sessionUpdate: "tool_call",
+          toolCallId: "tc-stale",
+          title: "Stale retry tool",
+          status: "pending",
+        },
+      });
+      return Promise.reject(new Error("cancel unsupported"));
+    });
+
+    await session.cancel();
+    await expect(turn).resolves.toBe("cancelled");
+    expect(session.getStatus()).toBe("idle");
+
+    emitChunk("agent_message_chunk", " retry after cancel");
+    const firstAnswer = session.store
+      .getDisplayMessages()
+      .find((message) => message.sender === AI_SENDER);
+    expect(firstAnswer?.message).toBe("partial answer");
+    expect(firstAnswer?.parts).toEqual(
+      expect.arrayContaining([
+        expect.objectContaining({ kind: "thought", text: "initial thought" }),
+      ])
+    );
+    expect(firstAnswer?.parts?.some((part) => part.kind === "tool_call")).toBe(false);
+    expect(firstAnswer?.turnStopReason).toBe("cancelled");
+
+    const next = session.sendPrompt("second");
+    expect(mock.prompt).toHaveBeenCalledTimes(1);
+    emitChunk("agent_message_chunk", " stale retry", "msg-retry");
+
+    jest.useFakeTimers();
+    try {
+      resolveBackingPrompt!({ stopReason: "cancelled" });
+      await jest.advanceTimersByTimeAsync(500);
+      emitChunk("agent_message_chunk", " delayed stale retry", "msg-retry");
+      await jest.advanceTimersByTimeAsync(500);
+      expect(mock.prompt).toHaveBeenCalledTimes(1);
+
+      await jest.advanceTimersByTimeAsync(1_000);
+      expect(mock.prompt).toHaveBeenCalledTimes(2);
+      emitChunk("agent_message_chunk", " stale trailing chunk", "msg-retry");
+      emitChunk("agent_message_chunk", "recovered", "msg-second");
+      resolveSecondPrompt!({ stopReason: "end_turn" });
+      await expect(next.turn).resolves.toBe("end_turn");
+      expect(session.store.getDisplayMessages().at(-1)?.message).toBe("recovered");
+    } finally {
+      jest.useRealTimers();
+    }
+  });
 });
 
 describe("withReadOnlyPreamble", () => {

src/agentMode/session/AgentSession.ts

@@ -25,6 +25,7 @@ import {
   PlanSummary,
   PromptContent,
   PromptInput,
+  PromptOutput,
   SessionEvent,
   SessionId,
   SessionUsage,
@@ -84,6 +85,10 @@ export const DEFAULT_TITLE_PREFIX = "New session";
  * agent's own context always receives the full output regardless.
  */
 const MAX_TOOL_OUTPUT_TEXT_CHARS = 256_000;
+// ACP prompt results can arrive before the last session/update frames. Require
+// a quiet interval after a cancelled backing prompt settles before dispatching
+// a follow-up on the same session.
+const CANCELLED_TURN_QUIET_MS = 1_000;
 // Shared sentinel so `getPendingToolPermissions()` returns a stable reference
 // when nothing is pending — preserves React `useState` setter bail-out
 // behavior on idle subscription ticks.
@@ -376,6 +381,12 @@ export class AgentSession {
   // a newer turn's placeholder. Replaced on the next completion, cleared on
   // cancel/dispose.
   private settledStream: { placeholderId: string; messageIds: Set<string> } | null = null;
+  // A locally-cancelled prompt whose backend promise has not settled yet. A
+  // follow-up may be composed immediately, but its backend prompt waits on this
+  // barrier so output from the cancelled generation cannot target the new turn.
+  private cancelledPromptDrain: Promise<void> | null = null;
+  private cancelledTurnActivity = 0;
+  private cancelledMessageIds = new Set<string>();
   private abortController: AbortController | null = null;
   private listeners = new Set<AgentSessionListener>();
   private unregisterSessionHandler: (() => void) | null = null;
@@ -1002,7 +1013,18 @@ export class AgentSession {
   ): Promise<StopReason> {
     const placeholderId = this.placeholderId;
     const sessionId = this.backendSessionId!;
+    const signal = this.abortController!.signal;
     try {
+      const priorPromptDrain = this.cancelledPromptDrain;
+      if (priorPromptDrain) {
+        await Promise.race([
+          priorPromptDrain,
+          new Promise<void>((resolve) => {
+            signal.addEventListener("abort", () => resolve(), { once: true });
+          }),
+        ]);
+      }
+
       // Extract live Web Viewer content (reader-mode markdown, YouTube
       // transcripts) just before the prompt is built so it reflects the page
       // at send/flush time, not at compose time. Only take the async hop when
@@ -1083,7 +1105,39 @@ export class AgentSession {
         sessionId,
         prompt: promptBlocks,
       };
-      const resp = await this.backend.prompt(req);
+      const promptStarted = !signal.aborted;
+      let resp: PromptOutput = { stopReason: "cancelled" };
+      if (promptStarted) {
+        const backingPrompt = this.backend.prompt(req);
+        resp = await Promise.race([
+          backingPrompt,
+          new Promise<PromptOutput>((resolve) => {
+            signal.addEventListener("abort", () => resolve({ stopReason: "cancelled" }), {
+              once: true,
+            });
+          }),
+        ]);
+        if (signal.aborted) {
+          const settledPrompt = backingPrompt.then(
+            () => undefined,
+            () => undefined
+          );
+          const drain = settledPrompt.then(async () => {
+            let activity: number;
+            do {
+              activity = this.cancelledTurnActivity;
+              await new Promise<void>((resolve) =>
+                window.setTimeout(resolve, CANCELLED_TURN_QUIET_MS)
+              );
+            } while (activity !== this.cancelledTurnActivity);
+          });
+          this.cancelledPromptDrain = drain;
+          void drain.then(() => {
+            if (this.cancelledPromptDrain === drain) this.cancelledPromptDrain = null;
+          });
+          resp = { stopReason: "cancelled" };
+        }
+      }
       // Flush the buffer only on a non-cancelled completion — only then has the
       // backend durably ingested the `<prior_turns>` block. A cancelled prompt may
       // have stopped before ingesting it, so keep and re-inject (a duplicate is
@@ -1095,13 +1149,13 @@ export class AgentSession {
       // the turn, so a hard `prompt()` failure (transport/auth) leaves the flag
       // unset and the user's retry re-delivers the context (a user cancel still
       // resolves here, and the prompt did reach the backend, so it counts as delivered).
-      if (isFirstTurn) this.firstPromptSent = true;
+      if (isFirstTurn && promptStarted) this.firstPromptSent = true;
       // Same delivery contract as `firstPromptSent`: the note reached the backend
       // in this accepted (possibly cancelled) prompt, so advance the session's
       // cursor. A hard `prompt()` failure throws before here, leaving the cursor
       // unmoved so the retry re-delivers the note. Fan-out returns earlier and
       // never reaches this ack.
-      if (projectContextUpdates) {
+      if (projectContextUpdates && promptStarted) {
         this.markProjectContextUpdatesDeliveredFn?.(projectContextUpdates.epoch);
       }
       if (
@@ -1266,9 +1320,9 @@ export class AgentSession {
   }
 
   /**
-   * Cancel any in-flight turn. The backend may still emit a few trailing
-   * session events before the prompt promise resolves with
-   * `stopReason: "cancelled"` — that's expected.
+   * Cancel any in-flight turn. Local cancellation settles the prompt even if
+   * the backend ignores ACP `session/cancel`; the backend notification still
+   * runs so a compliant agent can stop work and keep its session reusable.
    *
    * Flushes any pending tool-permission and AskUserQuestion resolvers (rejects
    * / empty answers respectively) so the inline cards disappear immediately
@@ -1279,6 +1333,10 @@ export class AgentSession {
     const status = this.getStatus();
     if (status !== "running" && status !== "awaiting_permission") return;
     if (!this.backendSessionId) return;
+    this.abortController?.abort();
+    this.settledStream = null;
+    for (const messageId of this.currentMessageIds) this.cancelledMessageIds.add(messageId);
+    this.currentMessageIds = new Set();
     if (this.pendingToolResolvers.size > 0) {
       this.flushResolvers(this.pendingToolResolvers);
       this.notifyMessages();
@@ -1292,7 +1350,6 @@ export class AgentSession {
     } catch (e) {
       logWarn(`[AgentMode] cancel notification failed`, e);
     }
-    this.abortController?.abort();
   }
 
   /** Detach from the backend. Does not cancel — call `cancel()` first. */
@@ -1308,6 +1365,8 @@ export class AgentSession {
     this.currentTodoList = null;
     this.currentTodoListSignature = null;
     this.settledStream = null;
+    this.cancelledPromptDrain = null;
+    this.cancelledMessageIds.clear();
     this.currentMessageIds = new Set();
     // Fire the `"closed"` transition before clearing listeners so
     // subscribers still observe it. `disposed = true` above guarantees
@@ -1618,6 +1677,27 @@ export class AgentSession {
   private handleSessionEvent(event: SessionEvent): void {
     const update = event.update;
 
+    if (this.cancelledPromptDrain || this.abortController?.signal.aborted) {
+      switch (update.sessionUpdate) {
+        case "agent_message_chunk":
+        case "agent_thought_chunk":
+          this.cancelledTurnActivity += 1;
+          if (update.messageId) this.cancelledMessageIds.add(update.messageId);
+          logWarn(
+            `[AgentMode] dropping ${update.sessionUpdate} from cancelled turn ${this.internalId}`
+          );
+          return;
+        case "tool_call":
+        case "tool_call_update":
+        case "plan":
+          this.cancelledTurnActivity += 1;
+          logWarn(
+            `[AgentMode] dropping ${update.sessionUpdate} from cancelled turn ${this.internalId}`
+          );
+          return;
+      }
+    }
+
     // Refresh the live todo snapshot before any placeholder gating — the
     // snapshot is session-scoped state, not part of the message trail.
     if (update.sessionUpdate === "plan" && this.applyCurrentTodoList(update.entries)) {
@@ -1742,6 +1822,13 @@ export class AgentSession {
    * when there's no message to append to (a genuinely stray update).
    */
   private resolveContentTarget(messageId: string | undefined): string | null {
+    if (
+      this.cancelledPromptDrain ||
+      this.abortController?.signal.aborted ||
+      (messageId !== undefined && this.cancelledMessageIds.has(messageId))
+    ) {
+      return null;
+    }
     if (messageId && this.settledStream?.messageIds.has(messageId)) {
       return this.settledStream.placeholderId;
     }

src/constants.ts

@@ -935,15 +935,14 @@ export const RESTRICTION_MESSAGES = {
     `${extension.toUpperCase()} files are not supported in the current mode.`,
 } as const;
 
-export const OPENCODE_PINNED_VERSION = "1.15.13";
+export const OPENCODE_PINNED_VERSION = "1.16.0";
 export const OPENCODE_RELEASE_TAG = `v${OPENCODE_PINNED_VERSION}`;
 /**
- * Minimum opencode the plugin supports. v1.15.13 (PR sst/opencode#29929,
- * "promote next ACP implementation") dropped the dedicated ACP `models` state
- * and moved the model catalog to a `category:"model"` config option; older
- * binaries report no models to our picker, so we force an upgrade.
+ * Minimum opencode the plugin supports. v1.15.13 introduced the config-option
+ * model catalog we consume, and v1.16.0 made ACP `session/cancel` abort the
+ * backing turn so a stopped session remains reusable.
  */
-export const OPENCODE_MIN_ACP_VERSION = "1.15.13";
+export const OPENCODE_MIN_ACP_VERSION = "1.16.0";
 export const OPENCODE_RELEASE_URL_TEMPLATE =
   "https://github.com/sst/opencode/releases/download/v{version}/{asset}";
 export const OPENCODE_RELEASE_API_URL_TEMPLATE =