fix: retain resolved ACP execution timeout metadata (#14986)

## Thinking Path

> - Paperclip manages agent work through adapters and heartbeat runs.
> - ACP adapters resolve a timeout for the selected execution target.
> - An untouched sandbox timeout uses a four-hour default.
> - Heartbeat finalization rebuilt the metadata from the stored zero.
> - This made a timed-out sandbox run report an effective timeout of
zero.
> - This change retains the adapter's resolved policy for accurate run
diagnostics.

## Linked Issues or Issue Description

**What happened?**

ACP sandbox runs with `timeoutSec: 0` use the four-hour default. Their
terminal metadata reports `effectiveTimeoutSec: 0` and `timeoutSource:
config` because heartbeat finalization only reads the stored agent
configuration.

**Expected behavior**

The result must report the policy the adapter used: `14400` and
`sandbox_default`. Explicit limits, fractional limits, explicit
unlimited overrides, and local defaults must keep their resolved values.

**Steps to reproduce**

Run an ACP adapter on a sandbox target with `timeoutSec: 0`. Compare the
start log's four-hour policy with the terminal result's effective
timeout. The new tests exercise the adapter result and the heartbeat
metadata merge without waiting four hours.

**Paperclip version or commit**

Reproduced from `6eaf218924f0a89faf1c02eb0d6877a6c5c8a2cb`.

**Deployment mode**

Self-hosted server with an ACP sandbox execution target.

Searched open timeout and metadata issues and PRs. Related #14804
exposes timeout configuration in forms; #14496 proposes a default
policy; #14833 addresses CLI session retention. This PR changes only ACP
result metadata.

## What Changed

- Retain the resolved timeout in the ACP result after settlement.
- Use validated adapter resolution when merging terminal timeout
metadata. Preserve config fallbacks for older adapters and the HTTP
millisecond policy.
- Test sandbox defaults, explicit and fractional limits, explicit
unlimited overrides, local defaults, malformed metadata, and unchanged
cancellation fields.
- Document the result fields and their meaning.

## Verification

- `pnpm -r typecheck` passed.
- `pnpm build` passed.
- Stop metadata tests: 23 passed.
- Reporter and diagnostic suites: 84 passed; two real-Sentry-SDK tests
skipped because the optional SDK is not installed.
- ACP engine suite: all 206 tests passed with a deterministic local
`gemini --version` shim. Ambient host CLI probes made the existing
Gemini session-resume fixture intermittent (one assertion failure in
each of two broad runs); an isolated 15-case rerun and the clean-base
206-test suite also passed. No assertion or timeout was changed.
- `pnpm test:run` is in progress. This PR does not claim a complete
local suite pass.
- Independent review found no blocking issues. The tests cover real
adapter emission and the real metadata merge separately.

## Risks

Low runtime risk: this changes result diagnostics. It does not change
timeout values, cancellation acknowledgement, cleanup, checkpoint
safety, retries, or provider operations. It does not fix the cause of a
quiet or long-running tool. Older stored results are not rewritten. The
new source values apply only when an adapter returns a valid resolution.

## Model Used

OpenAI GPT-6 with reasoning, repository inspection, code editing, and
test execution. The deployment-specific model ID and context-window size
are not exposed in this session.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [ ] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [ ] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

Co-authored-by: Paperclip <noreply@paperclip.ing>

packages/adapter-utils/src/acpx-engine/execute.test.ts

@@ -2974,6 +2974,9 @@ describe("gemini ACP flag selection", () => {
     expect(explicitZero.runtimeOptions[0]?.timeoutMs).toBe(
       DEFAULT_REMOTE_SANDBOX_ADAPTER_TIMEOUT_SEC * 1000,
     );
+    expect(explicitZero.result.resultJson?.adapterExecutionTimeout).toEqual({
+      timeoutSec: DEFAULT_REMOTE_SANDBOX_ADAPTER_TIMEOUT_SEC, source: "sandbox_default",
+    });
 
     // A negative timeoutSec is the documented opt-out from any adapter
     // wall-clock timeout, sandbox targets included.
@@ -2982,6 +2985,7 @@ describe("gemini ACP flag selection", () => {
       sandboxContext,
     );
     expect(negativeOptOut.runtimeOptions[0]?.timeoutMs).toBeUndefined();
+    expect(negativeOptOut.result.resultJson?.adapterExecutionTimeout).toEqual({ timeoutSec: 0, source: "configured" });
     const startLine = negativeOptOut.logs.find(
       (entry) => entry.stream === "stderr" && entry.text.includes("Adapter execution timeout:"),
     );
@@ -3047,6 +3051,7 @@ describe("gemini ACP flag selection", () => {
       "Set adapterConfig.timeoutSec to raise it.";
     expect(result.timedOut).toBe(true);
     expect(result.errorCode).toBe("acpx_timeout");
+    expect(result.resultJson?.adapterExecutionTimeout).toEqual({ timeoutSec: 1, source: "configured" });
     expect(result.errorMessage).toBe(expectedMessage);
     expect(cancelReasons).toContain(expectedMessage);
     expect(result.resultJson).toMatchObject({ acpObservedEventCount: 0, acpPendingToolCount: 0, acpToolInventoryComplete: true });

packages/adapter-utils/src/acpx-engine/execute.ts

@@ -5483,6 +5483,15 @@ export function createAcpxEngineExecutor(deps: AcpxEngineExecutorOptions = {}) {
               } },
             };
           }
+          // Preserve the policy resolved for this execution target. The server
+          // cannot reconstruct sandbox defaults from the stored agent config.
+          capturedResult = {
+            ...capturedResult,
+            resultJson: {
+              ...capturedResult.resultJson,
+              adapterExecutionTimeout: { ...prepared.timeoutResolution },
+            },
+          };
           // The sync-back settlement step runs before this reproduces the result
           // (settlement precedes reproduction), so a failed workspace restore is
           // already recorded by the time we get here. Merge it into `resultJson`