fix: preserve message edits across timeline windows

[agent-p1p]

Fixes #419

Summary

• Moves kind-1009 edit folding from batch-local mapping into MessageTimelineStore, so standalone edit deltas can update an existing row and pending edits survive timeline-window replacement/pagination.
• Keeps unedited base rows plus bounded edit candidates keyed by edit event, validates target kind/author before rendering, and restores the next valid edit or original body on removal/invalidation/deletion.
• Preserves normal chat-body normalization and Markdown fallback behavior for edited plaintext.

Regression coverage

• standalone edit-only projection delta
• target and edit arriving in different windows
• newest edit ordering and fallback after retraction
• invalidated/deleted edit retraction
• forged-sender rejection, including a 200-edit pending flood
• trim, clear, target removal, replacement, and body normalization

Verification

• git diff --check — pass
• added-line security/debug scan — pass
• conflict-marker scan — pass
• added Swift lines over 120 columns — none
• signed commit verified with git verify-commit
• bash scripts/ci/macos-sanity-checks.sh — not runnable on this Linux host (xcodebuild: command not found); macOS CI is the authoritative compile/test run

Sensitive paths

None.

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Summary by CodeRabbit

• New Features

  • Added support for message edits in timeline updates and live projections.
  • Edited messages now display updated text while preserving reactions, replies, and other message details.
  • Edit overlays are validated by author and can fall back to earlier edits or the original message.

• Bug Fixes

  • Fixed edit-only timeline updates not appearing immediately.
  • Correctly handles invalidated, deleted, retracted, and whitespace-only edits.

• Tests

  • Added comprehensive coverage for edit application, reversion, validation, and window changes.

[coderabbitai]

Walkthrough

Message edit records are now decoded into persistent mutations and applied by MessageTimelineStore. Timeline windows and live projections pass these mutations through the store, allowing edits to affect targets across pagination, replacements, removals, and standalone edit updates.

Changes

Timeline edit overlay projection

Layer / File(s)	Summary
Decode edit overlays and apply edited content whitenoise-mac/Core/MarmotMapping.swift, whitenoise-mac/Models/MessengerModels.swift	Adds edit mutation and overlay types, removes batch-local edit folding from timeline mapping, and adds MessageItem.applyingEdit(plaintext:).
Rebuild rendered timeline state whitenoise-mac/Core/WorkspaceState.swift	Separates base messages from edit candidates, applies validity and preference rules, and recomputes rendered messages within the window limit.
Thread mutations through timeline updates whitenoise-mac/Core/WorkspaceState+Timeline.swift	Passes edit mutations through authoritative window replacement and live projection updates, including edit-only deltas.
Validate overlay lifecycle whitenoise-macTests/PureValueTests.swift	Tests overlay application, sender validation, persistence, retraction, clearing, retention, and plaintext normalization.
Validate timeline integration whitenoise-macTests/whitenoise_macTests.swift	Tests store-based folding, invalidation and deletion behavior, and standalone edit projections against existing targets.

Estimated code review effort: 4 (Complex) | ~45 minutes

Possibly related PRs

• marmot-protocol/whitenoise-mac#95: Both changes modify timeline record conversion and MessageItem.timeline(...) handling.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The changes implement cross-window and standalone edit folding as required by #419, with regression tests covering the described cases.
Out of Scope Changes check	✅ Passed	The added types, store refactor, model helper, and tests all support edit preservation; no unrelated scope is evident.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: preserving message edits across timeline windows.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch pip/whitenoise-mac-419

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[stage-review]

Ready to review this PR? Stage has broken it down into 4 individual chapters for you:

	Title
1	Define message edit mutation models
2	Implement edit state management in MessageTimelineStore
3	Wire edit mutations through WorkspaceState
4	Verify edit persistence and security

_{Chapters generated by Stage for commit d7bfca5 on Jul 13, 2026 12:41pm UTC.}

[agent-p1p]

CI blocker: master is red on messageMediaDiskCacheReadDeletionMaintainsTrackedFootprint() after #444; tracked as #457. The same failure reproduces on base SHA 0454dbf (run 29100021269) and twice on this branch after all #419 tests passed. This PR has therefore been red and is not merge-eligible under Pip policy. After #457 lands, rebase the final tree and open a fresh replacement PR; close this one once the replacement is green.