fix(timeouts): raise sandbox wall-clock backstop to 4h and make acpx_local timeouts self-describing (#9232)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work
> - Agent runs execute through adapters (e.g. `acpx_local`), which can
run locally, over SSH, or inside sandbox execution targets, each with a
wall-clock execution timeout
> - Sandbox-backed runs defaulted to a 30-minute wall-clock backstop
(`DEFAULT_REMOTE_SANDBOX_ADAPTER_TIMEOUT_SEC = 1800`), which kills
healthy long agent runs that are still making progress — long before the
recovery watchdog's 4h critical threshold would even consider them stuck
> - On top of that, `acpx_local` resolved its timeout directly from
`adapterConfig.timeoutSec` instead of the shared execution-target
resolver, and its timeout failures surfaced as a bare `Timed out after
Ns` — giving operators no clue which timer fired or which knob raises it
> - This pull request raises the sandbox backstop to 4h (aligned with
the recovery watchdog), routes `acpx_local` through the shared timeout
resolver, logs the effective timeout and its source at run start, and
makes every timeout error message self-describing
> - The benefit is that long-running sandbox agent runs no longer die at
30 minutes, and when a wall-clock timeout does fire, the run log states
exactly which timer fired and how to configure it

## Linked Issues or Issue Description

Refs #4535 (related: wall-clock execution timeouts killing agent runs
that are still making progress — that issue covers a different hardcoded
600s timer, but the operator pain is the same).

No exact public issue exists for this one, so describing it in-PR:

**Bug:** A long sandbox-backed `acpx_local` agent run was killed with a
bare `Timed out after 1800s` even though the agent was actively working.

- **What happened:** The run hit the 30-minute
`DEFAULT_REMOTE_SANDBOX_ADAPTER_TIMEOUT_SEC` backstop. `acpx_local`
never consulted the shared execution-target timeout resolution (it read
`adapterConfig.timeoutSec` directly, default 0), so on sandbox targets
the sandbox-provider default applied with no adapter-level say. The
resulting error named neither the timer that fired nor the knob that
controls it.
- **Expected:** Healthy long runs should not be killed by a 30-minute
wall-clock backstop when the recovery watchdog only treats runs as
critically stuck after 4h of output silence; and any timeout error
should say which timeout fired and how to raise it.
- **Impact:** Long, legitimate agent runs in sandboxes fail mid-work;
operators waste time reverse-engineering which of several timers
produced "Timed out after Ns".

## What Changed

- `packages/adapter-utils/src/execution-target.ts`
- `DEFAULT_REMOTE_SANDBOX_ADAPTER_TIMEOUT_SEC` raised from `1_800` to
`14_400` (4h), with a comment explaining it intentionally matches the
recovery watchdog's `ACTIVE_RUN_OUTPUT_CRITICAL_THRESHOLD_MS` (4h) so
the adapter backstop never fires before the watchdog path.
Output-inactivity monitors remain the primary hang detectors.
- New `resolveAdapterExecutionTargetTimeout(target,
configuredTimeoutSec)` returns `{ timeoutSec, source }` where `source`
is `configured` / `sandbox_default` / `unlimited`. The existing
`resolveAdapterExecutionTargetTimeoutSec` is preserved as a thin
wrapper, so current callers are unaffected.
- New `formatAdapterExecutionTimeoutErrorMessage(resolution)` and
`formatAdapterExecutionTimeoutStartLogLine(resolution)` produce
self-describing messages that name the timer that fired and the
`adapterConfig.timeoutSec` knob that controls it.
- `packages/adapters/acpx-local/src/server/execute.ts`
- `buildRuntime` now resolves the wall-clock timeout through the shared
resolver: sandbox targets default to the 4h backstop, local/SSH keep the
historical "0 = no adapter timeout", and a configured
`adapterConfig.timeoutSec` always wins.
- The executor logs the effective timeout and its source at run start
(`[paperclip] Adapter execution timeout: …`), so a later timeout is
diagnosable from the run log alone.
- All three bare timeout messages (timer cancel reason, turn result
`errorMessage`, catch-path `messageOverride`) now use the
self-describing format.
- `packages/adapters/acpx-local/src/index.ts` — the adapter
configuration doc for `timeoutSec` states the sandbox default and that
the output-inactivity monitor remains the primary hang detector.
- Tests: `packages/adapter-utils/src/execution-target-sandbox.test.ts`
and `packages/adapters/acpx-local/src/server/execute.test.ts` (see
Verification).

## Verification

- `pnpm --filter @paperclipai/adapter-utils typecheck` — passes
- `pnpm --filter @paperclipai/adapter-acpx-local typecheck` — passes
- `npx vitest run
packages/adapter-utils/src/execution-target-sandbox.test.ts
packages/adapters/acpx-local/src/server/execute.test.ts` — 2 files, 40
tests, all pass
- New/updated test coverage:
- sandbox default resolves to 4h (and the constant is asserted to be `4
* 60 * 60`)
- `resolveAdapterExecutionTargetTimeout` reports `configured` /
`sandbox_default` / `unlimited` sources with the correct precedence
(configured > sandbox default; local/SSH stay unlimited)
- exact wording of the self-describing error message and the
start-of-run log line
- `acpx_local` runtime picks up the sandbox default into `timeoutMs`,
keeps the unlimited local default, honors configured-over-default
precedence, emits the start-of-run log line, and surfaces the
self-describing `errorMessage`/cancel reason when the wall-clock timer
kills a turn

## Risks

- **Behavioral shift:** sandbox-backed adapter runs that previously hit
the 30-minute backstop now run up to 4h before the adapter kills them.
Genuinely hung runs are still caught much earlier by the adapters'
output-inactivity monitors and by the recovery watchdog; the wall-clock
timer is a last-resort kill switch. Operators who relied on the
30-minute default can restore it explicitly via
`adapterConfig.timeoutSec`.
- **Error-message consumers:** any tooling that pattern-matched the
exact `Timed out after Ns` string from `acpx_local` will see the new
self-describing message instead.
- No API or schema changes; `resolveAdapterExecutionTargetTimeoutSec`
keeps its exact signature and behavior (modulo the raised sandbox
default).

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- Claude (Anthropic) via Claude Code CLI — model ID `claude-fable-5`,
extended thinking enabled, agentic tool use (file edits, shell, test
execution)

## 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
- [x] 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
- [ ] 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>

docs/agents-runtime.md

@@ -66,7 +66,7 @@ In agent runtime settings, configure heartbeat policy:
 For local adapters, set:
 
 - `cwd` (working directory)
-- `timeoutSec` (max runtime per heartbeat)
+- `timeoutSec` (max runtime per heartbeat; `0` uses the target default — no adapter timeout on local/SSH, a 4-hour backstop on sandbox targets — and a negative value disables the adapter timeout everywhere, including sandboxes)
 - `graceSec` (time before force-kill after timeout/cancel)
 - optional env vars and extra CLI args
 - use **Test environment** in agent configuration to run adapter-specific diagnostics before saving