test(mergeQueue): cover queueState, enqueue, dequeue and enqueuedByBot directly

[hivecommons-hive]

Description

Adds __tests__/utils/mergeQueue.test.ts, a direct unit test for src/utils/mergeQueue.ts (queueState, enqueue, dequeue, enqueuedByBot, and the private classify/errorMessage helpers). Until now this module was exercised only indirectly through the tide handler tests and the bundle e2e suite, both of which drive it through fixtures that always return a populated repository.pullRequest and an enqueue entry with a position.

New assertions, none of which existed in either suite:

• queueState returns undefined — without a warning — when GitHub answers repository.pullRequest: null or repository: null (src/utils/mergeQueue.ts:96, the file's only uncovered line on main)
• queueState warns once per run on a GraphQL failure, stays quiet on the next call, and warns again after resetMergeQueueWarnings(); a transport (non-GraphQL) failure is reported by its message
• entry mapping with and without an enqueuer, and no entry key when the PR is not queued
• enqueue returns { ok: true } with no position when the mutation returns a null entry or a null payload
• every classify kind (head_moved, already_queued, not_ready, forbidden, other) pinned to representative GitHub messages
• errorMessage joins several GraphQL errors[].message, and falls back to the thrown error's message when none carries one
• dequeue success and a refused dequeue (warns, returns false)
• enqueuedByBot: github-actions case-insensitively, any [bot] suffix, humans, look-alikes, undefined

Test-only change; no src/ or dist/ changes, so no repack is needed.

Closes #189

Testing

• npx vitest run __tests__/utils/mergeQueue.test.ts --coverage --coverage.include=src/utils/mergeQueue.ts → 33 passed; mergeQueue.ts | 100 | 96.66 | 100 | 100 (remaining branch is the String(e) fallback for a non-Error throw, which octokit never produces)
• npx eslint __tests__/utils/mergeQueue.test.ts → clean

Checklist

• I ran npm run all to lint and build my code (lint + tests; no build/pack output changes since only __tests__/ is touched)
• I ran npm run pack and committed dist/ — n/a, no source change
• Commits are signed off (DCO)
• Note any new dependencies these changes bring in — none
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation — n/a
• My changes generates no new warnings

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Disjoint from the open test PRs #173/#175/#177/#179/#181/#183/#185/#187: this PR adds one new file, __tests__/utils/mergeQueue.test.ts, and touches no existing test.

Filed by quality agent (hold-gated mode). Human review required.

— hive: agent=quality backend=copilot model=claude-fable-5.1 copilot=1.0.88

[hivecommons-hive]

Important

Held for human review by the hive's ACMM level gate.

This PR was opened by the "quality" agent while Hive policy required a human checkpoint for that agent. Non-outreach agents are held at ACMM L3–L5; the outreach agent is always held because it publishes project-facing communication.

Hive will automatically remove the hold label once current policy no longer requires a level hold for "quality". If this is an outreach PR, a human must review it and remove the label.

[github-actions]

Please add a kind label with /kind failing-test or /kind cleanup.