perf(extension): inject Mergify merge-box row before network state arrives

[jd]

Previously the row was the very last thing to appear in the merge box on
cold loads — the user would see GitHub's "Squash and merge" panel for
seconds before the Mergify "Add to merge queue" button materialised.
The reason is that _tryInject awaited four network roundtrips in
sequence before building the row:

1. /search?q=…mergify.yml (is Mergify enabled on this repo?)
2. fetchCommentBodies (stack/revision context)
3. /{org}/{repo}/pull/{n}/checks (find the queue check-run ID)
4. /{org}/{repo}/runs/{check_run_id} (resolve "queued" vs "evaluating")

Reorder so the row appears as soon as the merge box exists:

• The is-Mergify-enabled check now tries the synchronous detection path
  first (Mergify app-icon in the DOM or a cached repo result). The
  /search fetch is only paid on the rare cold load where Mergify has
  not yet commented on the page.
• The initial row is built with state derived synchronously from the
  DOM (deriveQueueButtonState reads open/merged/closed, the expanded
  Checks section if present, and the last @mergifyio command — all
  sync), then injected immediately into the merge box.
• renderMergifyContext and fetchQueueStateIfNeeded now run in
  parallel as background fire-and-forgets. When the queue-state fetch
  resolves, a then() callback runs updateMergifyRow, which swaps
  the button in place if its data-mergify-queue-btn attribute
  changed — no full row rebuild.
• The merge-box DOM-walking is extracted into injectRowIntoMergeBox()
  to keep the new early-injection path readable.

Trade-off: on a PR that is queued, when the Checks section has not
been expanded, the button briefly shows "Add to merge queue" before
flipping to "Remove from merge queue" once the network state arrives.
This is a single-button swap, not a row reflow.

Co-Authored-By: Claude Opus 4.7 (1M context) noreply@anthropic.com

Depends-On: #475

[jd]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	feat(extension): rework merge-box queue row to match GitHub native styling	#475
2	perf(extension): inject Mergify merge-box row before network state arrives	#476	👈

[mergify]

Merge Protections

Your pull request matches the following merge protections and will not be merged until they are valid.

🔴 ⛓️ Depends-On Requirements

Waiting for

• depends-on=Mergifyio/browser-extension#475 [⛓️ feat(extension): rework merge-box queue row to match GitHub native styling #475 [stack]]

This rule is failing.

Requirement based on the presence of Depends-On in the body of the pull request

• depends-on=Mergifyio/browser-extension#475 [⛓️ feat(extension): rework merge-box queue row to match GitHub native styling #475 [stack]]

🔴 Required Reviews

Waiting for

• #approved-reviews-by >= 2

This rule is failing.

• any of:
  • #approved-reviews-by >= 2
  • author = dependabot[bot]

🟢 Enforce conventional commit

Wonderful, this rule succeeded.

Make sure that we follow https://www.conventionalcommits.org/en/v1.0.0/

• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert|ui)(?:\(.+\))?:

🟢 🔎 Reviews

Wonderful, this rule succeeded.

• #changes-requested-reviews-by = 0
• #review-requested = 0
• #review-threads-unresolved = 0

🟢 📕 PR description

Wonderful, this rule succeeded.

• body ~= (?ms:.{48,})

[jd]

Revision history

#	Type	Changes	Reason	Date
1	initial	e57f72e		2026-05-20 10:15 UTC
2	rebase	e57f72e → 053c047 (rebase only)		2026-05-20 10:15 UTC