ci: parallelize real-api e2e files

docs/rfc/implemented/testing/2026-06-19-real-api-e2e-ci.md

@@ -20,7 +20,7 @@ ci.yml's value is that it is keyless, forkable, and always-green: any contributo
 
 ### Cost is not the constraint; reliability is
 
-The usual reason to ration real-API CI — token cost — does not apply here: we are DeepSeek and internal inference is effectively free. So the design optimizes for *coverage and signal*, not for minimizing calls. The suite runs in full (all six `*.e2e.ts` files), on multiple triggers, on every trusted PR. This is the CI embodiment of the [docs/testing.md](../../../testing.md) with-key policy.
+The usual reason to ration real-API CI — token cost — does not apply here: we are DeepSeek and internal inference is effectively free. So the design optimizes for *coverage and signal*, not for minimizing calls. The suite runs in full (all matching `*.e2e.ts` files), on multiple triggers, on every trusted PR. This is the CI embodiment of the [docs/testing.md](../../../testing.md) with-key policy.
 
 ### Triggers: trusted events only
 
@@ -54,7 +54,7 @@ The repo secret is named `DEEPSEEK_API_KEY_EXTERNAL`; it is mapped to the `DEEPS
 
 ### Scope, runtime shape
 
-Run **only** `test:e2e`. The keyless gates (typecheck/lint/coverage/snapshot/build/hygiene) already run in ci.yml on every push and PR; repeating them here would duplicate signal and slow the real-API job. No build step — e2e tests run unbuilt via tsx + the tsconfig paths map. Single Node 24 (the `engines` floor): these tests exercise *API integration*, not node-version compat, which ci.yml's `[24, 26]` matrix already owns; a second Node version would double real-API calls for no added signal. `timeout-minutes: 45` bounds a wedged run given serial files (`fileParallelism: false`), 120s/test, and `retry: 2`. `cancel-in-progress` is enabled only for `pull_request` runs — a superseded PR run is on a stale commit and worth cancelling, whereas a push/schedule run is already producing the post-merge/nightly signal and is never cancelled.
+Run **only** `test:e2e`. The keyless gates (typecheck/lint/coverage/snapshot/build/hygiene) already run in ci.yml on every push and PR; repeating them here would duplicate signal and slow the real-API job. No build step — e2e tests run unbuilt via tsx + the tsconfig paths map. Single Node 24 (the `engines` floor): these tests exercise *API integration*, not node-version compat, which ci.yml's `[24, 26]` matrix already owns; a second Node version would double real-API calls for no added signal. `vitest.e2e.config.ts` runs files through a bounded worker pool (`DSH_E2E_MAX_WORKERS`, default and CI value `4`) so CI and local with-key runs parallelize independent files while retaining a one-line serial escape hatch for quota investigations. `timeout-minutes: 45` bounds a wedged run given 120s/test and `retry: 2`. `cancel-in-progress` is enabled only for `pull_request` runs — a superseded PR run is on a stale commit and worth cancelling, whereas a push/schedule run is already producing the post-merge/nightly signal and is never cancelled.
 
 ## Security