fix(ci): run the Windows suite in a single fork (the bounded pool was not enough)

The `--maxWorkers=2` fix from the previous commit was falsified by real CI:
run 34574847774 still ended with `[vitest-pool]: Worker forks emitted error /
Worker exited unexpectedly` while reporting 126 of 127 files passed and zero
FAIL lines. The worker that died was the one running
tests/native-surface.spec.ts — it produced NO results at all, which is the
same shape as the two earlier crashes (125/126 and 123/124: N-1 files
reported plus a silent worker exit at teardown).

So the consistent signature across all four crashes is a worker-recycling
race, not a test failure. `test:windows` now runs the whole suite in ONE fork
(`--maxWorkers=1`), which removes recycling entirely; the cost is wall-clock
(14 s -> 41 s locally, and the Windows step stays well inside its 30-minute
budget) and the signal is unchanged. Retries are still deliberately not used —
they would hide a real regression instead of removing the race.

The CI comment now records both Windows failure classes with their evidence,
so the next person can tell what this flag is for.

.github/workflows/ci.yml

@@ -92,16 +92,26 @@ jobs:
         run: pnpm typecheck
       - name: Lint
         run: pnpm lint
-      # `test:windows` caps the fork pool at 2 instead of `pnpm test`'s
-      # unbounded default. Five specs in this suite really start processes
-      # (tests/agent-pty, pty-deps, pty-helpers, install-powershell,
-      # smoke): node-pty's ConPTY helper and a cold `powershell.exe` are
-      # both console-bound, and this 2-core runner made parallel spawning
-      # the amplifier behind every red `Test` step in the 2026-09-09/10
-      # window — six real 5000 ms timeouts (agent-pty `:71`/`:106`,
-      # install-powershell `:105`, the latter measuring 12.1 s) and two
-      # silent vitest worker deaths. The test bodies now carry their own
-      # explicit timeouts as well; this just stops them starving each other.
+      # `test:windows` runs the whole suite in ONE fork (`--maxWorkers=1`),
+      # not `pnpm test`'s unbounded pool. Two distinct Windows-only failures
+      # motivated it, both recorded in docs/plans/2026-09-10-dsh-0.1.5-rc.2-adaptation.md:
+      #
+      #   1. Six red runs were real 5000 ms vitest timeouts in specs that
+      #      really start a process (tests/agent-pty:71/:106,
+      #      tests/install-powershell:105 — a cold powershell.exe start
+      #      measured 12.1 s, tests/git.spec.ts:85 at 9.6 s). The suite now
+      #      declares its own budgets (global testTimeout 15 s, 30 s in the
+      #      two heaviest describes), and serial execution stops the
+      #      process-spawning specs starving each other on a 2-core runner.
+      #   2. Four runs died at teardown with `[vitest-pool]: Worker forks
+      #      emitted error / Worker exited unexpectedly` while reporting
+      #      N-1 of N files passed and zero FAIL lines — a worker recycling
+      #      race, not a test failure. It survived --maxWorkers=2, so the
+      #      lane now recycles nothing at all.
+      #
+      # No retries: they would hide a real regression instead of removing the
+      # race. The cost is wall-clock (the Windows step runs several minutes
+      # against a 30-minute job budget), not signal.
       - name: Test
         run: pnpm test:windows
       - name: Build