perf(extension): render stack surfaces from localStorage cache before network

[jd]

Mirror the merge-box queue-row speedup for the stack context panel and the
floating stack-nav pill. Previously both surfaces only appeared after
renderMergifyContext finished its full network walk:

1. Find Mergify comment IDs (DOM scan or fetch the ~500KB Conversation HTML
   on the Files tab).
2. Fetch each comment body (4 parallel workers).
3. Parse stack + revision markers.

The in-memory caches (_commentBodyCache, _remoteCommentIdsCache) only
help within a single SPA session — they're lost on every hard reload, so
each cold load re-paid the full network walk before either surface drew
anything.

Add a localStorage-backed StackContextCache (1h TTL, keyed by
org/repo/PR) that stores the parsed stackData and revisionData —
both already plain JSON-serializable objects produced by
parseStackMarker / parseRevisionMarker. renderMergifyContext now:

• Reads the cache synchronously and, on hit, builds + injects the panel
  and nav immediately. The surfaces are on screen before the comment
  fetches even start.
• Continues the existing network refresh path. injectContextPanel
  and injectStackNav already dedupe via data-mergify-hash, so when
  the fresh data matches the cached render the second injection is a
  no-op. When it differs, the surfaces are swapped in place.
• Invalidates the cache when the fresh fetch reports no Mergify
  comments or no panel content, so a stale entry doesn't keep showing
  after the stack is dismantled upstream.

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

[mergify]

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[Copilot]

Pull request overview

Adds a localStorage-backed cache to render the Mergify stack context panel and floating stack navigation pill immediately on cold loads, then refreshes from the network and updates the cache.

Changes:

• Introduce StackContextCache (localStorage, 1h TTL) to persist parsed stack + revision data by org/repo/PR.
• Update renderMergifyContext to render from cache synchronously before starting the network comment walk, then refresh and update/invalidate the cache.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
src/stacks.js	Uses StackContextCache for cache-first rendering and cache update/invalidation during renderMergifyContext.
src/cache.js	Adds StackContextCache implementation backed by localStorage with TTL and remove/update helpers.

Comments suppressed due to low confidence (2)

src/stacks.js:758

• Cache invalidation on !panel is potentially too aggressive: parseStackMarker can return null for transient reasons (e.g., it explicitly rejects markers that don't match the current PR when stale DOM IDs are fetched during SPA navigation). In that case, removing the localStorage entry discards the last-known-good cache and defeats the cache-first speedup on the next tick. Consider only removing the cache when you have a strong signal the stack is gone (e.g., bodies.length === 0 or none of the fetched bodies contain either marker prefix), and otherwise keep the cached entry while still removing surfaces for this tick.

    const stackData = parseStackMarker(bodies, currentPull.number);
    const revisionData = parseRevisionMarker(bodies, currentPull.number);
    const panel = buildContextPanel(stackData, revisionData, currentPull);
    if (!panel) {
        _stackContextCache.remove(
            currentPull.org,
            currentPull.repo,
            currentPull.number,
        );
        removeContextSurfaces(currentPull);

src/cache.js:132

• get() treats entries with a missing/invalid timestamp as non-expiring because Date.now() - data.timestamp becomes NaN and the TTL check never triggers. It would be safer to validate timestamp is a finite number and treat anything else as expired (removing the key) to avoid sticky stale cache entries.

        try {
            const raw = localStorage.getItem(k);
            if (!raw) return null;
            const data = JSON.parse(raw);
            if (Date.now() - data.timestamp > this.expirationMs) {
                localStorage.removeItem(k);
                return null;
            }
            return {
                stackData: data.stackData ?? null,
                revisionData: data.revisionData ?? null,
            };

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[jd]

Revision history

#	Type	Changes	Reason	Date
1	initial	ff77f7c		2026-05-20 13:58 UTC
2	content	ff77f7c → 6fe7f18 (raw)	address review #479: wrap cache-first render in try/catch and discard the entry on shape mismatch (Copilot gc6Dfqot); export StackContextCache and add 7 unit tests mirroring PrStatusCache coverage (C…	2026-05-20 13:58 UTC

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-05-22 15:04 UTC · Rule: default
• ✅ Checks passed · on draft merge queue: embarking main (0ec99e4) and #479 together #489
• ✅ Merged — 2026-05-22 15:07 UTC · at 6fe7f18d8ad7933bc078e107b715f501406c6384 · squash

This pull request spent 2 minutes 18 seconds in the queue, including 1 minute 30 seconds running CI.

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