test(chromium): stop electron boot tests depending on host CDP ports

[latekvo]

Problem

boot-electron-spawn-error.test.ts fails intermittently with a single failure:

FAIL  test/boot-electron-spawn-error.test.ts > bootElectronApp — spawn error handling
      > rejects with a clear, actionable message when spawn emits ENOENT
Error: spawn ENOENT

It is not load, and it is not the timeout

I chased the obvious hypothesis first — vitest's 5000 ms default colliding with a ~3.5 s built-in wait — and it is wrong. Measured at origin/main before any edit:

condition	result
15 isolated runs	15/15 pass
10 concurrent copies	10/10 pass
3 full-suite runs (load avg 16)	3/3 pass
10 runs under sustained full-suite load (load avg 19-20)	10/10 pass

38/38, a 0% spontaneous failure rate. And the one test whose readyTimeoutMs is 5000 against vitest's 5000 ms default completes in 15-54 ms at load ~20 — a ~100x margin, nowhere near the boundary.

The real trigger, and it is deterministic

Anything on the host listening on the hardcoded CDP ports the test uses. Squatting one makes it fail 100% of the time:

squat 19223        →  Tests  1 failed | 8 passed (9)     ← the reported signature, exactly
squat 19222+19224  →  Tests  2 failed | 7 passed (9)
after this change  →  Tests  9 passed (9)   with 19223 still squatted

Mechanism. When a real endpoint answers, waitForCdpReady wins bootElectronApp's Promise.race in ~1 ms — long before the test's 10 ms setTimeout fires its synthetic error. The boot then resolves, detachBootListeners() removes the 'error' listener, and the test's child.emit("error", err) reaches a listener-less EventEmitter, so Node throws instead of the promise rejecting.

The source is correct throughout. The test binds a global shared resource it does not own, and 19222 is argent's own documented example CDP port — used in nine sibling test files and by every chromium-cdp-19222 device this repo's docs tell people to create. A developer with an Electron app open, or a second agent on the same machine, is enough.

Fix

One UNREACHABLE_CDP_PORT = 1 constant. Port 1 is privileged, so no unprivileged process can bind it and the probe cannot be answered by accident — the idiom three tests in this same file already used. Not a timeout widening.

Second defect, same file

This file was the only one of the three Electron boot tests that did not isolate port persistence, so its success-path boot wrote a real ephemeral port into the developer's actual ~/.argent/chromium-cdp-ports.json on every run. I watched it grow 55 → 56 → 91 entries across a session.

Both siblings already guard this — one mocks the module, the other redirects ARGENT_CHROMIUM_PORTS_FILE, with a comment stating tests "never touch the real" file. This file now redirects too. Verified by md5: before this change a run mutates the real file, after it the file is byte-identical.

Sibling fixed

chromium-discovery.test.ts asserted port 43211 was unreachable, but that sits inside Linux's ephemeral range (/proc/sys/net/ipv4/ip_local_port_range → 32768 60999), so a listen(0) fake CDP server in a parallel test file can legitimately be handed it. Same fix.

Left alone, verified safe: boot-electron-kill.test.ts, flows/flow-chromium-boot.test.ts, list-devices.test.ts — each owns its port via listen(0) or fully mocks the launcher. The fixed ports 43210, 54321, 54322 are only ever tracked or untracked, never network-probed.

Verification

• Deterministic repro above, reproduced at origin/main and re-run after the change with the squatter still live.
• Mutation: reverting the constant to 19223 with a squatter present fails four named tests — registers an 'error' listener…, rejects…ENOENT, rejects…EACCES, detaches BOTH boot listeners after a FAILURE path….
• Post-change: 15/15 isolated, 10/10 loaded, 10/10 concurrent.
• eslint . 0, prettier --check . 0, tsc --build 0 — unpiped, exit codes read directly.
• Full packages/tool-server: identical to the origin/main baseline over 3 runs. The 6 boot-device-hotboot failures on that baseline are a separate host-environment defect, fixed in test(tool-server): stop unit tests inheriting the developer's ARGENT_* overrides #707, not touched here.