fix(test): Bun proof scripts exit 0 on a failed assertion

[vivek7405]

Problem

Every test/bun/*.mjs proof script that boots a server through startServer exits 0 when its assertions fail under Bun, so CI reports green on a real regression.

Verified with a minimal repro (boot startServer, then assert.equal(1, 2)):

node t5.mjs  -> exit=1   (correct)
bun  t5.mjs  -> exit=0   (swallowed)

Cause: startServer calls installProcessHandlers (packages/server/src/listener-core.js L388), which registers an uncaughtException handler that runs the graceful shutdown, and makeShutdown ends in process.exit(0) on a clean close (L426). On Bun a top-level assertion failure in the module body routes through that handler, so the shutdown's exit code wins. Node reports the module-evaluation rejection before the handler can exit, which is why only Bun is affected in practice. The scripts pass a quiet logger, so the logged error is swallowed too and the run is completely silent.

Impact: .github/workflows/ci.yml runs roughly fifteen of these directly (run: bun test/bun/smoke.mjs, listener.mjs, compression.mjs, file-storage.mjs, app-boot.mjs, seed.mjs, blog-db.mjs, path-alias.mjs, timeouts.mjs, binding-prefixes.mjs, slot-ssr-parity.mjs, and others) and trusts the step's exit code. Those steps currently cannot fail.

Found while adding test/bun/forwarded-proto.mjs in #1091: its counterfactual (revert the fix, expect red) came back exit 0.

Not affected: node scripts/run-bun-tests.js, which spawns bun test <file> (L119) and classifies on both status and the reported fail count, so the *.test.mjs wrappers DO fail correctly there. The hole is specific to the direct plain-script CI steps.

Design / approach

Two candidate fixes, not mutually exclusive:

1. Per-script (the shape fix(server): honor X-Forwarded-Proto/Host on the Bun listener #1091 already uses): capture the failure, run cleanup, then process.exit(1) explicitly. Self-contained and obviously correct, but it must be repeated in every script and a new script can silently forget it.
2. Systemic: have the proof scripts opt out of the framework's process handlers, or give startServer a way not to install them (a test-only flag), or set process.exitCode = 1 before the shutdown handler runs. Preferred, since it fixes every existing script at once and cannot be forgotten by the next one.

Whichever is chosen, add a guard so this cannot silently regress: a meta-test that runs a deliberately-failing proof script under Bun and asserts a non-zero exit.

Implementation notes (for the implementing agent)

• Where to look: packages/server/src/listener-core.js installProcessHandlers() (L388) and makeShutdown() (L410 onward, the process.exit(0) at L426). The scripts themselves are test/bun/*.mjs; the CI steps are in .github/workflows/ci.yml around L104 to L204. The working counterexample to copy is test/bun/forwarded-proto.mjs (from fix(server): honor X-Forwarded-Proto/Host on the Bun listener #1091).
• Landmines:
  • Do NOT simply stop installing the handlers in production. They are the graceful-shutdown path (SIGINT/SIGTERM drain, the 10s force-exit) and are load-bearing for a real deploy.
  • installProcessHandlers is guarded by a globalThis.__webjsProcHandlers latch, so a second startServer in one process is a no-op. A per-test opt-out must account for that.
  • The scripts pass a quiet logger, so any fix that only logs remains invisible. The exit code is the contract.
  • Verify the fix on BOTH runtimes: node currently exits 1 and must keep doing so.
• Invariants: packages/ stays plain .js + JSDoc. Node/Bun parity (Support both Bun and Node runtimes (first-class create + run) #508) is the whole point of this test layer.
• Tests: a meta-test asserting a failing proof script exits non-zero under Bun. A counterfactual is inherent here (the test IS the counterfactual).

Acceptance criteria

• A test/bun/*.mjs proof whose assertion fails exits non-zero under Bun
• Node keeps exiting non-zero for the same failure
• Graceful shutdown on SIGINT/SIGTERM is unchanged for a real server
• A guard test prevents this from silently regressing
• The existing proof scripts are covered (systemic fix) or individually updated