Root cause: `getContextWindowUsage` caches the *promise* of
`fetchContextWindowUsage` in a per-session WeakMap keyed by client. When
`ctx.client.session.messages({ path: { id: sessionID } })` never settles
(observed once `service=session.processor ... error=Aborted process`
takes hold), the cached pending promise wedges every concurrent and
later caller in the same session. The five hooks that share one
`createDynamicTruncator(ctx)` -- directory-agents-injector,
directory-readme-injector, rules-injector, tool-output-truncator, plus
indirect callers -- all await that same poisoned promise on every Read,
so the user-facing tool chain hangs forever and ESC cannot break it.
Reporters in #4086 land on this path consistently when reading AGENTS.md
files (which trigger directory-agents-injector via the directory walk).
Fix: race the underlying `session.messages` call against a 5s timeout
through a new `withFetchTimeout` helper. On timeout the catch block logs
the failure and returns `null`, which `dynamicTruncate` already treats
as the "context usage unavailable" signal and falls back to the static
truncation budget. Successful responses still cache as before. The
`message.updated finish=true` invalidation hook still clears poisoned
caches on the next completed turn so retries are clean.
Tests:
- Add a never-settling `session.messages` mock with a 50 ms override via
the new `_setContextWindowUsageFetchTimeoutMsForTesting` hook (matches
the established `_setXxxForTesting` pattern in `opencode-http-api.ts`
and `prompt-async-gate.ts`).
- Three new BDD cases pin the fix: (1) single caller returns null fast,
(2) parallel concurrent callers all unblock on the same cached promise
instead of hanging, (3) invalidate + retry rehydrates cleanly.
- All 8 pre-existing tests in the file still pass (happy paths, cache
reuse, invalidation, env/model fallback).
Verification:
- `bun test src/shared/dynamic-truncator.test.ts` -- 11 pass.
- `bun test src/shared/prompt-async-route-audit.test.ts` -- 6 pass
(added log import, no raw prompt route added).
- `bun test` (full suite) -- 7009 pass, 1 skip, 1 pre-existing flake in
`closeTmuxPane` mock.module test (reproduces on dev without this
change; isolated run passes).
- `bun run typecheck` -- clean.
- `bun run build` -- clean (esm bundle + tsc + schema).
- Manual harness `.debugging/manual-qa.ts` (uncommitted) drives the same
shape as the real hook chain and resolves the hang scenario in 51 ms.
YeonGyu-Kim
67ead7bf6d