Edit and regenerate answer the edited message; restore files on rewind (#24)

[derekhearst]

Summary

Picked up the interrupted attempt (substantial uncommitted work), verified and hardened it, then finished tests, docs and commits. Edit and Regenerate no longer send the literal prompt 'regenerate' into the unedited SDK session. Every turn is now one streamed SDKUserMessage with a uuid we mint, recorded as the join on messages.metadata (sdkTurn on the user row, sdkTailUuid on the reply), so no migration was needed. A regenerate, including after an edit, sends the row's own text and attachments and resumes with resumeSessionAt at the previous reply's tail. That keeps the same session id and exactly the kept history. A cut the CLI refuses (for example one from before a compaction) is recognised before any model call and retried once on a fresh session primed with the kept history. File checkpointing is on for stable workspaces (a project or an agent persistentKey). A short-lived control session (resume, the run's cwd, enableFileCheckpointing, an input that never yields, no model call) runs rewindFiles dryRun for the preview and the real call on confirm. The restore dialog defaults on, lists the files with +/- totals, flags uncommitted files, needs an explicit overwrite for imported repos with uncommitted changes, and is hidden when there is nothing to restore. The server re-checks every guard, and a failed restore leaves the conversation unchanged. 'Compact Conversation' and the compaction before a model switch now send the SDK's /compact, and the switch notice is honest. The SDK behaviour was verified by running the bundled CLI against a stub Messages API: our uuid becomes the transcript uuid and the checkpoint key; the Write tool is checkpointed; resumeSessionAt drops the later turn and keeps the session id; /compact works as a plain-text prompt; a pre-compaction cut is refused with 'No message found'. The results are written up in docs/chat/chat.md.

After review: This round fixed all three should_fix items from the review. The branch still carries the earlier #24 work: file checkpointing, the rewind control session, and edit/regenerate cutting back the SDK session with resumeSessionAt. (1) Pending cut: editUserMessage and truncateAfterMessage now stamp the pivot row with metadata.sdkCutPending, in the same transaction as the cut. planTurn treats any turn in a conversation with a pending cut like a regenerate: it resumes at the previous reply's sdkTailUuid, keeps the same fresh fallback, and puts unanswered user rows after that reply in front of the text as a short preamble. Slash commands get no preamble, so /compact still works as a command. recordTurnJoin clears the stamp up to its row once the turn's session starts. So an edit whose stream POST fails, followed by a new message, no longer reaches the unedited session. (2) Finding 80 is now pinned. The /compact prompt and the model-switch notice moved into src/lib/chat/compact-command.ts, and the new tests/chat.compact.spec.ts pins the wording and a page-level click on Compact Conversation, asserting the POST content is exactly the /compact command with regenerate=false. (3) skippedLinks is passed through. applyMessageRewind reports filesRestored as the previewed files minus the skipped ones. BranchResult carries skippedLinks, and the page (one reportFileRestore line per handler) shows a dismissable notice rendered by RewindPreviewDialog, for example 'Restored 3 of 5 files. 2 were not restored: they are links...'. No migration was added. bun run check reports 0 errors and bun run build passes.

Closes #24

What was addressed

Audit findings (from the 2026-09-22 subsystem audit) were re-checked against the code before any change; "not a bug" means the claim did not hold up.

#	Item	Verdict	Note
should_fix:turn-plan.server.ts:41 (pending cut after failed edit stream)	should_fix:turn-plan.server.ts:41 (pending cut after failed edit stream)	fixed	Edit and regenerate stamp the pivot row with sdkCutPending in the cut transaction. planTurn cuts the next turn of any kind at the previous reply's tail, with an unanswered-rows preamble (none for slash commands) and the same fresh fallback. recordTurnJoin clears the stamp. Pinned in tests/chat.regenerate-fork.spec.ts: edit, then append U3 and plan a non-regenerate turn, then assert kind 'fork' with resumeSessionAt 'tail-1' and U2' in the preamble; after the join, the next message is 'continue'. Also pinned there: the regenerate stamp plus the /compact case, and clearing scoped to its own conve
should_fix:+page.svelte:1372 (finding 80 unpinned)	should_fix:+page.svelte:1372 (finding 80 unpinned)	fixed	New src/lib/chat/compact-command.ts (compactCommand, compactSwitchNotice) is used by both the Compact Conversation button and the compaction before a model switch. New tests/chat.compact.spec.ts pins the prompt, the success and failure notice wording, and a real UI click whose POST body content equals '/compact …' with regenerate=false. The spec passes on desktop and mobile; on desktop it sets a 1024px viewport, because the button only exists in the phone/tablet header.
should_fix:message-branch.server.ts:77 (skippedLinks dropped)	should_fix:message-branch.server.ts:77 (skippedLinks dropped)	fixed	ApplyRewindResult and BranchResult carry skippedLinks, and filesRestored is now the previewed count minus the skipped count (clamped). rewind-preview.ts restoreOutcomeNotice gives the wording. rewind-dialog.svelte.ts reportFileRestore sets state, and RewindPreviewDialog renders a dismissable top toast. Pinned by the regenerate-fork spec (a stub real rewind with skippedLinks: 2 gives filesRestored 1, skippedLinks 2) and the engine.rewind spec (wording).

Verification

• bun run check: 0 errors
• bun run build: passes
• Specs: Run with E2E_PORT=4511 and the e2e-port patch, which was applied and then reverted. Suites: tests/chat.turn-plan.spec.ts, tests/chat.regenerate-fork.spec.ts, tests/engine.rewind.spec.ts, tests/engine.turn-input.spec.ts, tests/chat.edit-regenerate.spec.ts, tests/chat.compact.spec.ts and tests/auth.remote-guards.spec.ts, on both desktop and mobile. Final run: 176 passed. One earlier combined run had a single failure on mobile in chat.edit-regenerate: editMessage returned 'Message not found'. It did not happen again in 12/12 repeat-each runs or in the next full 176/176 run. The probable cause is outside this change: tests/global-setup.ts deletes every 'E2E:%' row, and other branches run Playwright in parallel against the same shared dev database.
• Independent review: approve (0 must-fix, 3 should-fix), addressed in a follow-up round.

Docs updated

• docs/chat/chat.md
• docs/structure/parity-reaudit-2026-09-22.md
• docs/chat/spec.md (earlier commit)
• docs/context/spec.md (earlier commit)
• docs/structure/claude-desktop-parity.md (earlier commit)
• README.md (earlier commit)

Follow-ups / residual risk

1. The pending-cut stamp is cleared in recordTurnJoin, which runs when the SDK sends its first message (onSessionId), as the reviewer suggested. If a turn is aborted after that point but before the CLI appends the user entry, the cut could be lost. The window is very small; a stale stamp does little harm, because the cut is taken at the latest reply before the turn. 2) The skipped-links toast has no UI-level spec. Driving it needs a real CLI restore with a symlink in the dev server's session store. The wording and the server pass-through are pinned in the unit and module specs. 3) Minor review observations not addressed, as they were non-blocking: while the preview runs, a composer send gets a 409 and shows the generic 'A turn is already running…' text (the server's own error text could be surfaced); a /compact turn saves an assistant row with '(no output)'; regenerating a /compact row whose cut is refused still puts the history preamble in front of the command on the fresh fallback (the fork attempt now skips it); the Compact button shows even when there is no SDK session, and /compact might error there (unverified); session-usage over-counting after a truncating resume (already on main); old conversations with no join fall back to a lossy text preamble (getSessionMessages() could recover the tail uuid). 4) There is no Compact Conversation entry point at desktop width; the context ring with the button is only in the phone/tablet header. 5) tests/global-setup.ts deletes every 'E2E:%' row. That makes UI specs flaky when several branches run Playwright against the shared dev DB at the same time; one such flake was seen here.

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