feat(acp): add resumeSessionId to sessions_spawn for ACP session resume (#41847)

* feat(acp): add resumeSessionId to sessions_spawn for ACP session resume

Thread resumeSessionId through the ACP session spawn pipeline so agents
can resume existing sessions (e.g. a prior Codex conversation) instead
of starting fresh.

Flow: sessions_spawn tool → spawnAcpDirect → initializeSession →
ensureSession → acpx --resume-session flag → agent session/load

- Add resumeSessionId param to sessions-spawn-tool schema with
  description so agents can discover and use it
- Thread through SpawnAcpParams → AcpInitializeSessionInput →
  AcpRuntimeEnsureInput → acpx extension runtime
- Pass as --resume-session flag to acpx CLI
- Error hard (exit 4) on non-existent session, no silent fallback
- All new fields optional for backward compatibility

Depends on acpx >= 0.1.16 (openclaw/acpx#85, merged, pending release).

Tests: 26/26 pass (runtime + tool schema)
Verified e2e: Discord → sessions_spawn(resumeSessionId) → Codex
resumed session and recalled stored secret.

🤖 AI-assisted

* fix: guard resumeSessionId against non-ACP runtime

Add early-return error when resumeSessionId is passed without
runtime="acp" (mirrors existing streamTo guard). Without this,
the parameter is silently ignored and the agent gets a fresh
session instead of resuming.

Also update schema description to note the runtime=acp requirement.

Addresses Greptile review feedback.

* ACP: add changelog entry for session resume (#41847) (thanks @pejmanjohn)

---------

Co-authored-by: Pejman Pour-Moezzi <481729+pejmanjohn@users.noreply.github.com>
Co-authored-by: Onur <onur@textcortex.com>

extensions/acpx/src/runtime.test.ts

@@ -127,6 +127,32 @@ describe("AcpxRuntime", () => {
     expect(promptArgs).toContain("--approve-all");
   });
 
+  it("uses sessions new with --resume-session when resumeSessionId is provided", async () => {
+    const { runtime, logPath } = await createMockRuntimeFixture();
+    const resumeSessionId = "sid-resume-123";
+    const sessionKey = "agent:codex:acp:resume";
+    const handle = await runtime.ensureSession({
+      sessionKey,
+      agent: "codex",
+      mode: "persistent",
+      resumeSessionId,
+    });
+
+    expect(handle.backend).toBe("acpx");
+    expect(handle.acpxRecordId).toBe("rec-" + sessionKey);
+
+    const logs = await readMockRuntimeLogEntries(logPath);
+    expect(logs.some((entry) => entry.kind === "ensure")).toBe(false);
+    const resumeEntry = logs.find(
+      (entry) => entry.kind === "new" && String(entry.sessionName ?? "") === sessionKey,
+    );
+    expect(resumeEntry).toBeDefined();
+    const resumeArgs = (resumeEntry?.args as string[]) ?? [];
+    const resumeFlagIndex = resumeArgs.indexOf("--resume-session");
+    expect(resumeFlagIndex).toBeGreaterThanOrEqual(0);
+    expect(resumeArgs[resumeFlagIndex + 1]).toBe(resumeSessionId);
+  });
+
   it("serializes text plus image attachments into ACP prompt blocks", async () => {
     const { runtime, logPath } = await createMockRuntimeFixture();
 

extensions/acpx/src/runtime.ts

@@ -203,10 +203,14 @@ export class AcpxRuntime implements AcpRuntime {
     }
     const cwd = asTrimmedString(input.cwd) || this.config.cwd;
     const mode = input.mode;
+    const resumeSessionId = asTrimmedString(input.resumeSessionId);
+    const ensureSubcommand = resumeSessionId
+      ? ["sessions", "new", "--name", sessionName, "--resume-session", resumeSessionId]
+      : ["sessions", "ensure", "--name", sessionName];
     const ensureCommand = await this.buildVerbArgs({
       agent,
       cwd,
-      command: ["sessions", "ensure", "--name", sessionName],
+      command: ensureSubcommand,
     });
 
     let events = await this.runControlCommand({
@@ -221,7 +225,7 @@ export class AcpxRuntime implements AcpRuntime {
         asOptionalString(event.acpxRecordId),
     );
 
-    if (!ensuredEvent) {
+    if (!ensuredEvent && !resumeSessionId) {
       const newCommand = await this.buildVerbArgs({
         agent,
         cwd,
@@ -238,12 +242,14 @@ export class AcpxRuntime implements AcpRuntime {
           asOptionalString(event.acpxSessionId) ||
           asOptionalString(event.acpxRecordId),
       );
-      if (!ensuredEvent) {
-        throw new AcpRuntimeError(
-          "ACP_SESSION_INIT_FAILED",
-          `ACP session init failed: neither 'sessions ensure' nor 'sessions new' returned valid session identifiers for ${sessionName}.`,
-        );
-      }
+    }
+    if (!ensuredEvent) {
+      throw new AcpRuntimeError(
+        "ACP_SESSION_INIT_FAILED",
+        resumeSessionId
+          ? `ACP session init failed: 'sessions new --resume-session' returned no session identifiers for ${sessionName}.`
+          : `ACP session init failed: neither 'sessions ensure' nor 'sessions new' returned valid session identifiers for ${sessionName}.`,
+      );
     }
 
     const acpxRecordId = ensuredEvent ? asOptionalString(ensuredEvent.acpxRecordId) : undefined;