fix(amr): close ACP stdin on abort so vela tears down OpenCode (#3097)

* fix(amr): close ACP stdin on abort so vela tears down OpenCode

When an AMR (vela) run is cancelled, attachAcpSession.abort() sent a
`session/cancel` RPC but left the child's stdin open. The vela ACP bridge
keeps running until it sees EOF (or is signaled), and it only shuts down
its private OpenCode `serve` process on a clean exit — so on abort the
OpenCode server lingered until the caller's SIGTERM fallback, and leaked
entirely if the parent was killed before cleanup ran.

End stdin after sending the cancel (mirroring the clean-completion path)
so the agent receives EOF and shuts down its own runtime promptly,
independent of signal timing.

* fix(amr): end stdin on abort even before session/new resolves

Addresses review on #3097: abort() still returned early when sessionId
was unset, so the stdin EOF only happened after session/new completed.
Cancelling during ACP startup (before the session exists) left the
OpenCode-teardown window open until the caller's SIGTERM fallback — and a
parent hard-kill before that could still strand the private OpenCode
process.

Move stdin.end() out of the sessionId guard so abort always closes stdin
when the pipe is writable; gate only the session/cancel RPC on sessionId.
Add a regression test that aborts during startup and asserts stdin is
ended with no session/cancel emitted.

apps/daemon/src/acp.ts

@@ -701,12 +701,27 @@ export function attachAcpSession({
       aborted = true;
       finished = true;
       clearStageTimer();
-      if (!sessionId || !child.stdin || child.stdin.destroyed || child.stdin.writableEnded) return;
+      if (!child.stdin || child.stdin.destroyed || child.stdin.writableEnded)
+        return;
+      // Only cancel an established session; before session/new resolves there
+      // is no sessionId to cancel, but we must still close stdin below.
+      if (sessionId) {
+        try {
+          sendRpc(child.stdin, nextId, 'session/cancel', { sessionId });
+          nextId += 1;
+        } catch {
+          // The caller owns process-signal fallback if the ACP transport is gone.
+        }
+      }
+      // Always close stdin so the agent receives EOF and shuts down its own
+      // runtime — the vela ACP bridge tears down its private OpenCode server on
+      // EOF — instead of lingering (and leaking that server) until the caller's
+      // SIGTERM fallback fires. This also covers aborts during ACP startup,
+      // before session/new returns. Mirrors the clean-completion path above.
       try {
-        sendRpc(child.stdin, nextId, 'session/cancel', { sessionId });
-        nextId += 1;
+        child.stdin.end();
       } catch {
-        // The caller owns process-signal fallback if the ACP transport is gone.
+        // Best effort; the caller still owns the SIGTERM/SIGKILL fallback.
       }
     },
   };

apps/daemon/tests/acp.test.ts

@@ -231,6 +231,55 @@ test('attachAcpSession exposes abort and sends session cancel after session crea
   assert.deepEqual(cancelRequest.params, { sessionId: 'session-1' });
 });
 
+test('attachAcpSession.abort closes stdin so the agent shuts down on EOF', () => {
+  const child = new FakeAcpChild();
+
+  const session = attachAcpSession({
+    child: child as never,
+    prompt: 'hello',
+    cwd: '/tmp/od-project',
+    model: null,
+    mcpServers: [],
+    send: () => {},
+  });
+
+  child.stdout.write(`${JSON.stringify({ id: 1, result: {} })}\n`);
+  child.stdout.write(`${JSON.stringify({ id: 2, result: { sessionId: 'session-1' } })}\n`);
+
+  assert.equal(child.stdin.writableEnded, false);
+  session.abort();
+  // EOF on stdin lets the vela ACP bridge tear down its OpenCode server
+  // without waiting for the caller's SIGTERM fallback.
+  assert.equal(child.stdin.writableEnded, true);
+});
+
+test('attachAcpSession.abort during startup ends stdin without sending session/cancel', () => {
+  const child = new FakeAcpChild();
+  const writes: string[] = [];
+  child.stdin.on('data', (chunk) => writes.push(String(chunk)));
+
+  const session = attachAcpSession({
+    child: child as never,
+    prompt: 'hello',
+    cwd: '/tmp/od-project',
+    model: null,
+    mcpServers: [],
+    send: () => {},
+  });
+
+  // Abort before session/new resolves (no sessionId yet) — e.g. the user
+  // cancels during ACP startup. stdin must still close so OpenCode tears down.
+  assert.equal(child.stdin.writableEnded, false);
+  session.abort();
+  assert.equal(child.stdin.writableEnded, true);
+
+  // No session to cancel yet, so no session/cancel RPC should be emitted.
+  const cancelRequests = parseRpcWrites(writes).filter(
+    (entry) => entry.method === 'session/cancel',
+  );
+  assert.equal(cancelRequests.length, 0);
+});
+
 function parseRpcWrites(writes: string[]): Array<Record<string, unknown>> {
   return writes
     .join('')