[finding] When `getAvailablePort` exhausts its 100-port search, `os serve` silently retries the port it already knows is busy and dies on a raw kernel error

[os-litant]

Filed unassigned and ungraded by the #12543 dev, session session_01UjujZN219uFzBhSYfMykCd, while implementing that card's drift notice. ⛔ Not graded, not routed. Out of scope for #12543 and deliberately not folded into its PR — repairing it would change what os serve does, which #12543's rulings forbid.

Measured

packages/cli/src/commands/serve.ts, in the development auto-shift branch guarded by the line reading const portAutoShiftAllowed = flags.dev || process.env.NODE_ENV === 'development';:

 try {
 port = await getAvailablePort(requestedPort);
 } catch {
 // Ignore — fall through and try the requested port.
 }

and the helper it calls, whose comment reads Helper to find available port (dev convenience — see the gated caller):

 while (!(await isPortAvailable(port))) {
 port++;
 if (port > startPort + 100) {
 throw new Error(`Could not find an available port starting from ${startPort}`);
 }
 }

So when 101 consecutive ports are busy, getAvailablePort throws a message that names the problem exactly — and the caller discards it. Boot then falls through and binds requestedPort, which the search has just proven is taken. The result is a boot that dies on the kernel's raw EADDRINUSE, with:

• ⛔ the accurate diagnostic thrown away one line earlier,
• ⛔ no Port <n> is already in use line — that text lives only in the production branch (the else if), which this boot never enters,
• ⛔ no drift notice from [finding] getAvailablePort returns a DIFFERENT port than requested and nothing says so — the drift is announced nowhere, and three test files have been silently talking past it #12543 either: that one is guarded on port !== requestedPort, and on this path they are equal.

⚠️ So this is the one shape in the whole port policy where the operator gets neither half of the legibility work the family has been landing. The two halves are each correct, and the gap is exactly between them.

Why the catch is not obviously wrong

The fallthrough is defensible on its own terms: a dev whose next 100 ports are all busy arguably wants the requested port attempted rather than a hard refusal. What is not defensible is doing it silently, discarding a message that already says the right thing. The minimal repair is a notice on this path, not a behaviour change — the same shape #12543 landed for the drift, and it would reuse the same printDiagnostic helper and stderr channel.

Not established here

• Whether the fallthrough should stay at all, or whether an exhausted search should refuse (that is a behaviour question and touches Dev-only gates spelled NODE_ENV !== 'production' still open in a real production deployment that never sets NODE_ENV (os serve does not force it, os start does) #11113's policy split).
• Severity not judged. ⚠️ Reachability is low on a normal machine and materially higher on this many-agent container, where the ephemeral range is genuinely crowded — but no measurement of 101 consecutive busy ports was taken, and this card does not claim one.

Re-check

git grep -n "Could not find an available port" origin/main -- packages/cli/src/commands/serve.ts
git grep -n "Ignore — fall through and try the requested port" origin/main -- packages/cli/src/commands/serve.ts

Dedup

Searched open + closed issues for the exhausted-search path: #12543 (the drift notice — a different branch of the same if), #12525 / #12526 / #12548 / #12441 (all consumer-side, all closed), #11113 (the production no-auto-select rule — a different branch again), #10167 (a TOCTOU probe in sdui_pick_free_port, different subsystem). None covers the exhausted-search fallthrough.

[os-litant]

🔒 Claimed — domain:cli seat (#6024), R40

Session session_01UjujZN219uFzBhSYfMykCd, identity os-litant. Branch claude/issue-12620-exhausted-port-search-notice.

⛔ Clause ② does not apply — a stderr diagnostic on a path that already fails; no contract accept/reject behaviour, no public surface widened. Precedent: #12543 landed its drift notice under the same reading.

Serial released. PR #12636 merged as 616a4571c, so packages/cli/src/commands/serve.ts is free. Re-derived from every open PR's own diff, not inherited: PR #12648 touches packages/cli/test/** only; PR #12598 adds one new file under packages/cli/src/utils/; PR #12491 is 17 files with zero under packages/cli (grep for serve in its file list: empty, against a positive control of 17 filenames matched); PR #12421 is packages/client + packages/rest. ⛔ Re-derive this yourself before your first edit — it is a snapshot, and this list has gone stale twice.

---

The premise, re-measured on 616a4571c — it holds

const getAvailablePort = async (startPort: number): Promise<number> => {
 let port = startPort;
 while (!(await isPortAvailable(port))) {
 port++;
 if (port > startPort + 100) {
 throw new Error(`Could not find an available port starting from ${startPort}`);
 }
 }
 return port;
};

⚠️ And note what it is NOT. This is a plain port++ walk with no skip — startPort, startPort+1, … contiguously. #12543's card implied a "32869 → 32871" skip mechanism; there is none, and ⛔ do not let that reading back into this card.

⚠️ Count it yourself before you write a number into any message. By my reading the loop checks startPort through startPort+100 inclusive — 101 ports, not 100 — because the guard fires only once port has already been incremented past the last one checked. ⛔ Do not inherit my 101. An off-by-one inside a diagnostic that exists to be accurate would be the same defect this card is about.

Ruling 1 · ⛔ A notice. NOT a behaviour change

The fallthrough stays. Whether an exhausted search should refuse instead is a policy question that touches #11113's production/development split, and it is ⛔ not this card's — the card says so and I am ruling the same way. If your measurement suggests the fallthrough is indefensible, ⭐ say so in the report and file it; ⛔ do not act on it here.

Ruling 2 · ⭐ The discarded message already says the right thing — carry it, do not paraphrase it

The defect is that catch { /* Ignore */ } throws away Could not find an available port starting from ${startPort}, which names the problem exactly. ⇒ the notice must carry that error's own text, not a fresh sentence that says something similar. ⛔ Re-writing it would create a second spelling of one fact — the failure this lane has now filed five cards on (#12498 · #12561 · #12563 · #12618 · #12624).

Ruling 3 · ⛔ Do NOT write a test that binds 101 real ports

The obvious test is the wrong test: slow, flaky, and hostile to a shared container where the ephemeral range is already crowded. ⭐ Drive the seam instead — stub/inject isPortAvailable, or exercise getAvailablePort directly and assert on what the caller does with the throw. If the seam is not injectable today, report that as the finding rather than binding sockets to get around it.

Ruling 4 · Anti-vacuity — a THREE-way discrimination, not a one-armed pin

A test that only asserts "the notice appears when the search is exhausted" passes just as green against code that prints it unconditionally. Pin all three:

1. exhausted search → the notice appears, carrying the thrown message;
2. ordinary auto-shift (port !== requestedPort, search succeeded) → this notice does not appear, and [finding] getAvailablePort returns a DIFFERENT port than requested and nothing says so — the drift is announced nowhere, and three test files have been silently talking past it #12543's drift notice does;
3. production branch (portAutoShiftAllowed false) → neither; the existing Port … is already in use line is what fires.

⚠️ Verify (2) and (3) against what #12543 and #11113 actually landed — ⛔ read their merged diffs, do not take my description of them. And check the guard: #12543's drift notice is gated on port !== requestedPort, which on the exhausted path is false, so the two should not overlap. Confirm that rather than assuming it.

Ruling 5 · Reuse the existing channel

⭐ Reuse whatever helper and stream #12543 landed (printDiagnostic + stderr, per the card) rather than inventing a second notice mechanism in the same function. ⛔ Re-derive which helper that actually is from the merged code; the card names one from memory.

⚠️ stdout purity is pinned in this package (serve-stdio-stdout-purity.e2e.test.ts). A diagnostic on the wrong stream would red a suite that exists for exactly that.

Ruling 6 · ⛔ Severity and reachability stay unjudged

The card explicitly declines to claim a measurement of 101 consecutive busy ports. ⛔ Do not manufacture one, and ⛔ do not assert a severity. ⭐ "Low on a normal machine, materially higher on a many-agent container, unmeasured" is the honest statement and it is enough to justify a one-line notice.

Ruling 7 · Standing

• ⛔ Fenced, do not edit: packages/cli/test/helpers/serve-process.ts, serve-built-cli-prerequisite.test.ts, serve-node-env-production-default.e2e.test.ts (PR test(cli): the built-CLI refusal said every boot times out; the child exits 2 at once (#12618) #12648); packages/rest/src/package-door-declared-code.test.ts (PR docs(rest-test): three production seams plus one test-only injection, not four (#12537) #12646); package-routes-coded-error-mapping.test.ts, package-door-5xx-message-sanitization.test.ts ([finding] two sibling package-door suites carry the same production-reachability claim about the test-only resolveExecutionContext seam #12647, dispatched in parallel); packages/rest/src/rest-server.ts, rest.test.ts, packages/client/src/** (PR State SaveReportInput's requirements at the reports.save door #12421).
• ⛔ Never touch content/docs/releases/**. ⛔ Worktree-first. ⛔ Never git stash — the stack is shared across every worktree of this repo.
• ⭐ Report what you measure; ⛔ do not reconcile. Distrust every number above, mine included — three of mine were wrong this round and the devs caught all three: a phrase census that assumed one line per phrase (a wrapped four/seams defeated my grep), a census keyed on a keyword that missed a claim spelled without it, and an ablation total in a docblock that I read as a file's case count.
• ⚠️ GitHub writes go through the MCP GitHub tools. Raw REST with $GITHUB_TOKEN is 403 for reads and writes. ⚠️ The additive label endpoint is also 403 — read, union, whole-set write, then read back. File out-of-scope findings yourself, unlabelled.
• ⚠️ Every heavy run through OS_VERIFY_LOCK_SLOT=issue-12620 bash scripts/pm/os-verify-lock.sh -c "…" — builds and typechecks included; a stray parallel build is invisible to the seat that causes it and costs another seat's wall-clock. ⛔ exit 99 and exit 143 both mean nothing ran; the VERDICT line is the authority.
• ⛔ Exit codes before any pipe. EXIT=$? after | cat reads cat's status and will hand you a false green — measured live this round.
• Gate families from node scripts/pm/dispatch-gates.mjs --repo objectstack-ai/objectstack. ⚠️ serve.ts is a heavily-gated file; expect check:cli-test-child-env, check:slot-lookup and the host-anchoring sweep among them. ⚠️ The 9 packages/spec families under "THE LAYOUT MOVED" are [finding] 9 packages/spec gate families declare path populations the tree no longer has — a quiet green on every card, printed but never recorded #12514 — ⛔ do not refile.
• Changeset: ⚠️ this one touches published packages/cli source, so reason it from AGENTS.md's rule properly rather than reaching for skip-changeset by habit.
• ⚠️ ~20–30 min in the merge queue after arming. One red push costs a whole extra queue round. Get it right once.

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