fix(web-client): persist chat transcript across page reloads

[john-the-dev]

Summary

The web-UI conversation transcript (#transcript) was in-DOM only — append-only with no persistence and no restore-on-load — so reloading the page wiped the entire chat. The Tasks list survived (it persists via taskMap → loadPersistedTaskMap()), which is exactly why a reload left task entries visible but no chat bubbles, making it look like "history is gone."

This is a long-standing gap, not a new regression.

What changed (src/web-client.ts)

• Snapshot transcript entries to localStorage (sutando-transcript-v1), capped at the 50 most recent; oversized entries (e.g. data-URL images) are skipped to stay under the storage quota, with a halve-and-retry fallback on QuotaExceededError.
• Restore on DOMContentLoaded — recreate each bubble, sanitize stored html with DOMPurify, and re-attach a live copy button (the button's onclick can't survive an innerHTML round-trip, so it's stripped on snapshot and re-added on restore).
• A MutationObserver on #transcript captures every append path (text replies, voice transcripts, images) without editing each call site; snapshots are debounced (400ms) and suppressed during restore.

Interaction with #1856

#1856 (in-flight chat-send persistence) re-appends the user's pending message on load via resumePendingChatSends(). When both land, an in-flight send during a reload would render the user bubble twice (once from transcript-restore, once from resume). Trivial follow-up when the second of the two merges: drop the user-bubble re-append from resumePendingChatSends() since transcript-restore already covers it. No conflict today (separate branches off main).

Test plan

• npx tsc --noEmit passes
• Restarted the running web-client onto this code; served HTML contains the fix
• Manual: send/receive chat, reload page → transcript (user + assistant bubbles) is restored
• Manual: copy button on a restored assistant bubble works
• Manual: confirm no unbounded localStorage growth over a long session

Note: UI change — typechecked and smoke-verified the fix is served, but the manual reload behavior needs a human pass (owner is testing live).

🤖 Generated with Claude Code

[github-actions]

@cla-assistant check

[bassilkhilo-ag2]

✅ MutationObserver approach is the right way to capture all append paths without touching each call site. 400ms debounce avoids a snapshot per keyframe. TRANSCRIPT_MAX_ENTRY_LEN guard prevents data-URL images from blowing localStorage quota. DOMPurify used on restore. Approve.

[bassilkhilo-ag2]

Correct approach: MutationObserver on #transcript debounced at 400ms avoids spamming localStorage on every DOM append, and catches all write paths (text, voice transcript, image) without editing each call site. The quota-exceeded retry (halving the entry count) is practical. The _transcriptRestoring guard prevents the restore pass from triggering a snapshot write, avoiding a needless re-serialization on load. TRANSCRIPT_MAX_ENTRIES=50 and MAX_ENTRY_LEN=20000 are reasonable bounds. ✓

[bassilkhilo-ag2]

Transcript persistence is well-implemented. MutationObserver captures all append paths without touch-every-call-site. DOMPurify on restore is correct defense-in-depth. Quota-exceeded retry (slice to half), 20KB entry size limit, and _transcriptRestoring guard against snapshot feedback-loop are all good defensive choices. LGTM.