OG cards key on a 7-char SHA while permalinks key on the full SHA — the first unfurl never reuses the warm slot

[lukaso-bot]

Found by the review round on #144.

The OG image URL for a commit permalink is always built with a 7-character SHA:
ogImageUrl() → commitImageUrl(..., shortSha(result.canonicalSha), ...)
(packages/web/src/ui/og-meta.tsx:65; shortSha is sha.slice(0, 7) at :115).
So web-og calls /internal/result/:owner/:repo/<7 chars> and that endpoint computes
the cache key part sha:<7 chars>.

The public permalink route keys on the SHA as it appears in the request URL, and
/lookup deliberately redirects to the full SHA (packages/web/src/index.ts:138 —
"Use the FULL SHA in the permalink (not a 7-char prefix)").

Concrete flow, which is the primary search → view → share path:

1. A user searches honojs/hono@<40-char sha>.
2. They land on /r/honojs/hono/c/<40>, which warms cacheKey('res', repo, 'sha:<40>', 'cull', 'nopre').
3. They share that URL. The unfurl fetches the OG image, which resolves sha:<7> —
   a different slot. Still cold, still a full lookup.

#144 fixed the write-back half (the OG path now self-heals into sha:<7>, so it is cold
at most once) and made /internal use the public routes' key shape and policy. This is the
remaining half: the two sides spell the same commit two different ways, so a warm public
entry is never reused for the first unfurl.

Why it is not folded into #144

The fix lives in files #144 does not touch (ui/og-meta.tsx, routes/result.tsx), and
either direction changes the public routes' key namespace, which is a cache-invalidation
event for every existing entry and deserves its own review surface:

• Normalise to short on both sides — possible pre-lookup (sha.slice(0, 7)), but changes
  the public routes' cache key.
• Normalise to full on both sides — not possible pre-lookup for a 7-char input: you do not
  know canonicalSha until the lookup has run. Would need a second keyed write after resolve.

Short-on-both is the smaller change. Needs a test that seeds the slot a full-SHA permalink
writes and asserts the OG path reads that entry.