[leorfer23]

Follow-up to #99. Three cuts to the unit suite's module-loading cost.

• Slim test entry. wrangler.test.toml main → tests/worker-main.ts: only the DO classes, with ChatDO and Showtime stubbed. Those two pulled in the agent loop and the screenshot stack, ~8s on every file that touches a DO. session-do.test.ts (the only real ChatDO user) runs in a new workers-chat project whose main is still src/index.ts. DO tests: ~8s → ~3s each.
• Shared isolate for side-effect-free files. New workers-shared project runs with isolate: false. tests/isolation.ts puts a file there only if neither it nor any local helper it imports mocks modules, patches globals, fakes timers, or touches D1/DO bindings. A vitest-isolate comment opts a file out (used once: artifacts/member-view.test.ts). That's 228 files, and 6 runs of that set with file order shuffled were all green.
• source-timestamps.test.ts now reads src/ with fs in the node project instead of import.meta.glob inside workerd: 18s → 0.2s. It still fails on a planted datetime('now').
• Also rebuilds public/_bundles/skill.zip, which went stale on main after docs(blobs): list the MIME types the blob API actually allows #97 (docs change without a rebuild).

Measured (load 3–8, machine shared with other agents)

• Full suite: ~154s → 115–140s (one run took 190s under a load spike). Summed import time: 764s → ~600s.
• Full gate with all tests: 166s, all green.

Biggest remaining cost: ~300 isolated files that use vi.mock against route modules. They can't share an isolate without rewriting their mocks.

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