[teamleaderleo]

In a Claude chat, a Write that overwrote an existing file could be undone by moving that file to the Trash. The Claude translator sent every Write as an ACP diff with no old text, and the page reads a diff with no old text as a file the turn created. So the edited-files card's Undo offered "trash" for the overwritten file. The host would trash it, since the file still held the Write's text.

Now every Write diff starts out marked as a fragment (_meta.acpmux.fragment), which the page shows as "Cannot undo this edit" (edit_diffs in cmux-tui/crates/acpmux/src/claude_stdio/mod.rs). A shared settle_write removes the mark only when Claude Code's result confirms what the Write did:

• The Write created its file (type is create, or the result text reads "File created successfully at: …"): the mark is removed. The diff reads as a new file, and Undo may trash it.
• The Write overwrote a file, and the result names the same file and holds its old text (originalFile, up to 64,000 bytes, the same limit adopt uses): the diff takes that old text and loses the mark. Undo can then put the old text back.
• Anything else stays a fragment: an overwrite with no old text or an oversized one, a result for another file, a Write whose result never arrives (a crash, or a line dropped at the frame limit) and a refused permission.

Both paths run the same logic:

• Live: the tool_result line's tool_use_result, in inbound.rs.
• Adopted conversations: the transcript line's toolUseResult, passed through claude_tool_results into PastTool::settle (adopt_replay.rs, adopt_tools.rs).

Found while reviewing #23161. With that PR's page code, a confirmed create still shows as all added lines with Undo set to trash, and a Write still marked as a fragment shows no Undo. I checked this with a scratch jsdom test against #23161's head b2f24178bb3e.

Changelog

• Fixed: In cmux NEXT Claude chats, Undo no longer offers to move a file that a Write overwrote to the Trash, including in reopened conversations and for a Write whose result never arrived.

Tests

claude_stdio/edit_diff_tests.rs:

• the Write goes out as a fragment (updated claude_edit_write_is_a_whole_file_diff)
• no result: the call and its permission request stay fragments
• an overwrite with originalFile
• an overwrite with no structured result
• type: "update" with originalFile: null
• an originalFile over 64,000 bytes
• a created file, with and without the structured result
• a result for another file

adopt_tools.rs: an adopted Write that was created, overwritten with old text, overwritten with no structured result, and cut off before its result.

Fleet runs (scripts/ci/cmux-tui-rust-check.sh) at cbb54ec99d0:

• all write (step 59d5ecd11f642b2e7da5c97a): cargo fmt --check and clippy -D warnings pass, and 195 of 195 tests pass, including all 9 Write tests.
• test adopt: 86 run, 85 passed on the first try. durable_agents::an_adopted_claude_chat_still_moves_its_work_after_an_update_restart failed once and passed on its automatic solo rerun. It covers update restarts, not Write diffs.
• test claude_edit: 14 of 14 pass.

The first round's red run at 3a35056908b (tests only, step c212bed92cec8193d33a8486): the overwrite and other-file tests fail, and the created-file case passes.

Observed / Not run

• Observed: the fleet runs above, and the scratch page check against cmux NEXT: a one-file Edited card expands to its diff; View changes shows new and out-of-repo files #23161.
• Known: an overwrite that stays a fragment still shows its new text as added lines on the card ("+N -0"). It isn't marked as a new file and offers no Undo. Showing it without counts would be a webview change for a follow-up.
• Not run: the full cmux-tui suite. This PR's CI runs it.

Agent session: cosmic-gray
🤖 Generated with Claude Code

[teamleaderleo]

Owned by toolbar-diffviewer on cosmic-gray · session

[github-actions]

cmux status _{(one comment, edited in place; each line is updated by the job that owns it)}

Review cbb54ec: HQ feed card · gallery before/after runs · checks

App of this head (app.zip, kept 1 day)

gh workflow run reload-build.yml -R manaflow-ai/cmux --ref feat-cmux-next -f tag=pr23187 -f ref=cmux/write-undo-trash -f platform=macos -f backend_mode=local

red: cmux-next checks (god files, concurrency, crash safety, l10n); base red: the same failure on the base 1c367bb; does not block

[blacksmith-sh]

Found 6 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmp3o3eeezq/summary-fail.json (live):/summary-fail.json (live):	View Logs
/tmp/tmpem3hak6j/summary-missing.json (live):/summary-missing.json (live):	View Logs
convention violations found (ERROR lines above)./ convention violations found (ERROR lines above).	View Logs
test_a_pull_request_that_changes_the_shortcut_inputs_still_rewrites_them (main.Sett ingsOnlyArtifactLeavesTheActionFollowers.test_a_pull_request_that_changes_the_shortcut_ inputs_still_rewrites_them) (job='autofix')/ test_a_pull_request_that_changes_the_shortcut_inputs_still_rewrites_them (main.Sett ingsOnlyArtifactLeavesTheActionFollowers.test_a_pull_request_that_changes_the_shortcut_ inputs_still_rewrites_them) (job='autofix')	View Logs
test_regenerated_action_exports_bring_the_followers (main.SettingsOnlyArtifactLeave sTheActionFollowers.test_regenerated_action_exports_bring_the_followers) (job='autofix' )/ test_regenerated_action_exports_bring_the_followers (main.SettingsOnlyArtifactLeave sTheActionFollowers.test_regenerated_action_exports_bring_the_followers) (job='autofix' )	View Logs
test_settings_exports_alone (main.SettingsOnlyArtifactLeavesTheActionFollowers.test _settings_exports_alone) (job='autofix')/ test_settings_exports_alone (main.SettingsOnlyArtifactLeavesTheActionFollowers.test _settings_exports_alone) (job='autofix')	View Logs

^{Need help on this PR? Tag @codesmith-bot with what you need.}

[teamleaderleo]

Bead cx-80uhi created for this PR by the cmux coordinator.

[teamleaderleo]

cmux-tui SDKs / protocol contract is red on 8 of 8 fresh feat-cmux-next PR heads in the last 2:00:00, so it is most likely a base red, not this PR's. The base-reds lane has it; a base merge picks up the fix once it lands.

[cursor]

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[teamleaderleo]

Review (independent subagent, claude-opus-5-5): SHIP at cbb54ec

This re-review covers the PR's five files against merge-base 1c367bb. The base merge 6351b26 is excluded.

• Every path that delivers a Claude Write diff carries the fragment mark: the live call, the permission request (with_edit), a result that never arrives, and adopted and resumed sessions (via toolUseResult → PastTool::settle). No other crate builds Claude Write diffs; the hub, transcript, OptChat and iOS only display them.
• Clearing the mark removes _meta entirely, so toolDiffs sets no fragment. The completed update's content replaces the earlier diffs.
• The path match is exact string equality on toolUseResult.filePath (Claude Code 2.1.305 passes file_path through unchanged). A mismatch never borrows originalFile.
• Nothing else breaks: fragment is read only by fileUndo, and rendering still keys off oldText == null.

Non-blocking follow-ups:

• Claude Code reports type:"create" for a Write over an existing empty file, so Undo would move that empty file to the Trash, where it can be recovered.
• Undo writes originalFile back with LF line endings, which changes a CRLF file's endings.
• The "created" label on unconfirmed Writes is fixed in cmux NEXT: a one-file Edited card expands to its diff; View changes shows new and out-of-repo files #23161 (created: oldText == null && !fragment).

Agent session: cosmic-gray

[github-actions]

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.3960833477001 (4482e41d31)
• cmux NEXT nightly 1.0.0-nightly.3960894798201 (0b1a93e9c0)
• cmux NEXT nightly 1.0.0-nightly.3961101575901 (101cc33db2)