Parent

• #402 Acquire word-timed lyrics from AMLL, then fall back to LRCLIB

What to build

Songs that already have Line-timed Lyrics from an online source first-paint those lyrics, then receive a Word-timed Upgrade. The upgrade path calls AMLL only. A confident word-timed hit replaces the cache, resets offset, and lights karaoke fill. An ambiguous or empty AMLL result leaves the current lyrics in place and stamps a seven-day probe. Network errors do not stamp. Manual, sidecar, and embedded lyrics are not replaced by this upgrade. Unsynced embedded still uses the existing full-chain automatic upgrade.

Acceptance criteria

• First paint of cached lrc_lib / lrc_api / lrc_api_ttml is not blocked on AMLL.
• The session requests automatic_upgrade for those online line-timed sources when they have no word tokens, including unsynced lrc_lib. Protected sources stay skipped.
• Upgrade persist may replace those sources only with word-timed amll. A distinct probe-miss result must not share a type with “all online providers missing.”
• Merge gate: seed lrc_lib, drive the real AMLL-only persist path with AMLL 404 and with empty/ambiguous search; the row must stay lrc_lib and must not become absent.
• Successful miss/ambiguous stamps word_timed_checked_at (7-day TTL, same clock as negative cache). 429/5xx/timeout do not stamp. Clock failure treats the probe as fresh. An AMLL win clears the stamp.
• Stamp-only persist is a real change so Publish Changes copies the stamp. Upgrade miss keeps a user-tuned offset. Upgrade win resets offset.
• Session apply-filter ignores a non-amll follow-up when the current source is online line-timed.
• ADR 0027 records Word-timed Upgrade + confidence. ADR 0028 records no AGPL AMLL player packages. Contract fetch_lyrics_online semantics update.

Blocked by

• Ticket 3 (cold-path AMLL client, matcher, and accept-gate)