fix(core): size the win32 test deadline to the runners' cold-spawn tail, pin loop latency-additivity (#90)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

packages/core/vitest.config.ts

@@ -3,14 +3,30 @@
  * many core tests spawn a real shell (Git-Bash on the Windows CI runners) or write the
  * full Agent State layout, and Windows runner I/O variance (cold shell spawns, Defender
  * first-touch scans, slow-disk moments) has pushed individually fast tests past vitest's
- * 5s default — a different test on each run. A larger failure deadline changes nothing
- * for passing tests; POSIX keeps the 5s default to fail fast during local development.
+ * 5s default — a different test on each run.
+ *
+ * The deadline's first sizing (30s) turned out to be inside that variance tail: on one
+ * cold runner (PR #66's merge-ref run) the suite-start burst of first spawns across
+ * parallel workers put environment.test.ts's single-spawn write at 28.1s PASSING and
+ * engine.test.ts's first test at 35.7s FAILING, while runs of the same code minutes
+ * before and after finished the failing test in ~1.4s. The slowdown tracked OS work
+ * only — pure-JS test files stayed at normal speed in the same run — so the flow
+ * terminates and merely waits on the OS. Amplification confirms it: injecting spawn
+ * latency into the same test (a PENGUIN_SHELL shim sleeping before bash) reproduces the
+ * failure exactly at 30s injected vs the old 30s deadline, with the flow completing
+ * ~70ms after the spawn at every magnitude tried — tool latency flows through 1:1, the
+ * loop adds no waits of its own (pinned platform-neutrally by the "slow tool delays the
+ * run only by its own latency" test in test/engine.test.ts). 120s clears the observed
+ * tail with headroom while still bounding a genuinely hung test.
+ *
+ * A larger failure deadline changes nothing for passing tests; POSIX keeps the 5s
+ * default to fail fast during local development.
  */
 import { defineConfig } from "vitest/config";
 
 export default defineConfig({
   test: {
     environment: "node",
-    testTimeout: process.platform === "win32" ? 30_000 : 5_000,
+    testTimeout: process.platform === "win32" ? 120_000 : 5_000,
   },
 });