Went through all eight. Seven were right and are fixed in e532d37; I reproduced each one first rather than taking it on faith. One I am not taking, with reasoning below.

Fixed

Receipt capped by characters. Correct, and worse than described. Capping diff lines bounds nothing when one line is the whole file. Reproduced on a 200KB minified source:

before: file 200,007 bytes -> receipt 400,059 chars
after:  file 200,007 bytes -> receipt 481 chars

Characters are now capped per line and over the whole receipt.

replace_all as a non-boolean. Correct and the most dangerous of the set, since it silently corrupts. bool("false") is True, so the string turned the multi-match guard off and rewrote every occurrence:

before: replace_all="false" on 3 matches -> "Edited (3 replacements)", file became b\nb\nb
after:  replace_all="false" on 3 matches -> Error: matches 3 places ..., file untouched

"true" and "false" are mapped since models really do emit them; anything else is refused rather than guessed at.

Non-regular files. Correct, and it hangs rather than just misbehaving. A FIFO reports st_size 0 and then read() blocks forever, and this path has no timeout or cancel event, so the turn cannot be recovered. Confirmed with a 12s watchdog before the fix; now returns Error: 'pipe' is not a regular file. immediately.

Absolute paths already inside the workdir. Correct. With a workdir of /workspace/repo, /workspace/repo/a.py resolved to /workspace/repo/repo/a.py. Paths already contained by the workdir now skip the habit-path remap. I added a test that habit paths outside the workdir still remap, so the narrowing does not switch off the behaviour it narrows.

Concurrent edits. Correct. Reproduced two chats on a shared project workspace: the later rename discarded the earlier edit with no error. The bytes the edit was computed from are now compared again immediately before the rename, and a stale edit is refused with a message telling the model to re-read.

Containment at write time. Correct that checking the pathname once is not sufficient, since the whole read and diff sat between the check and the rename. Containment is now rechecked immediately before the rename, which removes that window. I want to be precise about what this does and does not do: it is a revalidation, not O_NOFOLLOW through directory descriptors, so it narrows the race rather than closing it. Doing it properly with dirfd semantics is worth its own change, needs a Windows story, and would apply equally to the existing python and terminal write paths, which have the same exposure today.

Not taking

Refuse creation whenever the target exists. The facts are right, the fix strands the model. Refusing every existing target makes a zero-byte file permanently unwritable through this tool: an empty old_string would be refused because the file exists, and no non-empty old_string can match an empty file, so both doors are shut.

empty file exists
  old_string=""  -> would be rejected under the suggested rule
  old_string="x" -> Error: 'old_string' was not found

On the metadata point, _edit_file_write already carries the mode over via copymode, and there are no contents to lose. I have made the behaviour explicit in a docstring and pinned it with a test so it reads as a decision rather than an oversight.

Deferred

__FILES__ envelope for created files. Real gap, but a feature rather than a defect: a file created through edit_file gets no download chip. It needs the sentinel wired on the backend and edit_file registered in the frontend's file-rendering set, and a half-wired sentinel leaks marker text to the model. It also only pays off in UI rendering that I would want to verify visually. Better as its own PR than bolted onto this one.

Also worth noting for whoever reviews: the envelope must only be emitted when the target is inside the session workdir, since under Full access edit_file can write anywhere and the UI can only serve sandbox files.

Testing

Ten new tests covering each fix, 36 in the file total, all passing. The wider tool and sandbox suites are unchanged: the same ten pre-existing failures on this branch as on a clean main (test_bypass_permissions.py::test_python_sandboxed_uses_sandbox_preexec_and_safe_env and nine in test_sandbox_files_and_storage_roots.py), and no new ones.

The red "Frontend build + bundle sanity" is a pre-existing flake, not this branch. Evidence below, since a red X on a PR is normally guilty until proven otherwise.

The two failures are:

not ok - HF hydration does not overwrite an in-flight user edit
not ok - cross-tab refresh replays after an active HF hydration

Both in tests/credential-persistence.test.ts, around hf-token-store. Nothing on this branch touches that module or anything it imports; the frontend files here are tool-status.ts, code-tool-placement.ts, chat-adapter.ts and message-response-details-sheet.tsx.

The assertions are the tell: one expects false and gets true, the other expects 2 fetch calls and gets 4. A doubled count is shared module state across test files, not a logic error.

It reproduces on demand under concurrency, on this branch:

run 1: pass 2278  fail 0
run 2: pass 2276  fail 2
run 3: pass 2276  fail 2
run 4: pass 2278  fail 0
run 5: pass 2278  fail 0

And, more to the point, on clean main with none of this branch's code, same two names:

main run 1: HF hydration does not overwrite an in-flight user edit; cross-tab refresh replays after an active HF hydration
main run 2: none
main run 3: none
main run 4: HF hydration does not overwrite an in-flight user edit; cross-tab refresh replays after an active HF hydration
main run 5: none
main run 6: none

Reproduce with node --experimental-strip-types --test --test-concurrency=8 "tests/**/*.test.ts" from studio/frontend, a few times. CI's default concurrency on a Linux runner hits it more often than a local single run does, which is why main mostly looks green.

Worth fixing on its own: the file leans on module singletons in hf-token-store and does not reset them between tests, so whether it passes depends on which file the runner schedules alongside it. Happy to open that separately rather than fold an unrelated fix in here.

For completeness, the earlier commit on this branch passed the same job (run 31755471343), which is the other thing you would expect from a flake rather than a regression. I have also kicked a re-run of the failed job with no code change.

Three more jobs went red as the matrix finished. I checked each rather than assuming they were all the same story as the frontend flake. None are from this branch.

Repo tests (CPU) -- one failure:

FAILED tests/studio/test_studio_text_descender_clipping.py::test_model_selector_trigger_label_uses_leading_tight
E   AssertionError: could not find ModelSelectorTrigger model-name span

Pre-existing on main. It passes on this branch in isolation and fails on a clean origin/main worktree at ea34ac9 with none of this branch's code, which is what CI is really testing since it builds the merge commit:

$ git worktree add /tmp/main-probe origin/main
$ pytest tests/studio/test_studio_text_descender_clipping.py
1 failed, 2 passed

Chat UI Tests -- not an assertion failure. The step "Drive model-picker per-model-config with Playwright" ends with ##[error]The operation was canceled. after 30m19s, so it hit the job timeout. Same model-picker area as the failure above.

Core (HF=latest + TRL=latest) -- tests/test_loss_normalization_contract.py::test_guard_returns_a_count_exactly_when_stock_transformers_would, plus a ModuleNotFoundError. That lane tracks upstream transformers/TRL releases and is training-side. This branch touches no training code; the diff is studio/backend/core/inference/, studio/backend/routes/inference.py and four Studio frontend files.

pip scan-packages :: hf-stack -- supply-chain scanner reporting evidence inside third-party packages (scipy CubicSpline, tokenizers byte_decoder). This branch adds no dependencies and changes no lockfile.

So the four reds are: one flake I reproduced on main, one test already failing on main, one timeout, and two dependency/training lanes unrelated to the diff. Worth someone looking at the model-picker pair independently, since that is two separate jobs pointing at the same component.

Second review pass: four new findings, all four correct and fixed in ae206c4. Reproduced each before changing anything.

Stop materializing the full diff. Right, and my earlier cap made it look fixed when it was not: I bounded the receipt's output while still feeding difflib the whole file and draining its generator into a list. Measured on a\n repeated to the 16MB cap with replace_all:

before: receipt 205 chars | RSS +501 MB | 1.3s
after:  receipt 201 chars | RSS  +48 MB | 0.05s

A 600KB file goes from +48MB to +1MB. Two separate bounds were needed, since either alone leaks: difflib is now fed only a window around the first change (found via before.find(old_string), so it is exact rather than a scan), and the generator is consumed with islice.

Windowing moves the hunk numbering onto the slice, so the headers are shifted back to real file lines. Otherwise a change at line 8000 reports as line 3:

Edited mid.py (1 replacement)
@@ -7998,5 +7998,5 @@
 line7999
-line8000
+CHANGED

Create without clobbering concurrent writers. Right, and it was a genuine hole rather than a theoretical one: I added the expect guard for edits and left the creation path on expect=None, so the one path that writes without reading first had no guard at all. The absent case is now O_EXCL (plus O_NOFOLLOW), so the loser of a race gets an error instead of silently overwriting; filling a zero-byte file goes through the normal guarded write with expect=b"".

Worth noting the sequential case already looked fine, which is exactly why it needed the atomic primitive rather than a better check.

Normal permissions for created files. Right. mkstemp makes the temp file 0600 and copymode had no existing file to copy from, so every file created through the tool landed 0600:

before: 0o600
after:  0o644   (0o666 & ~umask)

Fixed as a consequence of the O_EXCL change above, which takes the mode directly.

Document it in the public request schema. Right, and I had missed the second half of it. enabled_tools now lists edit_file, and bypass_permissions now says that Full access lifts its containment too, not just the python/terminal sandbox. Both are pinned by tests that read the field descriptions off ChatCompletionRequest, so a reword cannot silently drop them.

Testing. Eight new tests, 44 in the file, all passing. The wider tool and sandbox suites are unchanged from the same pre-existing baseline as before: test_bypass_permissions.py::test_python_sandboxed_uses_sandbox_preexec_and_safe_env, nine in test_sandbox_files_and_storage_roots.py, and the test_studio_api.py ones that need a live server. No new failures.

Review summary

Verdict: useful, merge after the fixes below (pushed as e7b3b90).

Before / after

Before, edit_file did not exist. Changing one line meant the model re-emitting the whole file through python or a shell heredoc. After, an exact-string replacement plus a bounded receipt. Measured on a 500-line file:

Real issue, not a fake one, on two independent counts: the token blowup above, and silent corruption - anything the model fails to retype in a whole-file rewrite is simply gone, whereas here a missing or ambiguous old_string is a hard error that writes nothing.

Does it break anything

No regressions. Full Studio backend suite at head 24095 passed / 163 failed, at the merge base 24048 / 160. The +47 are this PR's own tests; the 3-failure delta is a test_transformers_version.py / test_stt_ggml_sidecar.py ordering flake under -n 8 that gives an identical 5 failed, 344 passed on both head and base when run in isolation. _is_outside_workdir, the containment primitive, is byte-identical to base and was already used by the python/terminal path-healing, so no existing pathway changed.

Old installs: a caller that never sends edit_file is unaffected, and enabled_tools is a plain List[str] with no enum, so unknown names are ignored rather than rejected. New frontend against an old backend sends "edit_file" and the old backend ignores it - no 422. An old frontend rendering a new persisted chat falls through to the safe default glyph, never a throw. edit_file is an append to _FULL_ACCESS_TOOL_BY_NAME, not a substitution, and is_high_risk_tool_call("edit_file", ...) returns True, so Full access still prompts.

Three bugs found and fixed

All three were live at head, and all three mislead the model rather than crash - the worst failure mode for a tool the model cannot see the result of any other way.

1. The receipt invented deletions that never happened. _edit_file_receipt cut a window out of the before text and a second window of the same line count out of the after text. Any edit changing the line count shifts everything below it, so the two windows ended on different text and difflib reported the misalignment as a second hunk. Reproduced on a 400-line file:

@@ -317,4 +318,3 @@
 line317
 line318
-line319

line319 is still in the file, 119 lines from anything the edit touched. The receipt is the only thing the model learns about its edit, so a model that trusts it "restores" a line that never left. Fixed by cutting one window from the old text and replaying the replacement on it.

2. edit_file hung forever on a FIFO. The edit path had the S_ISREG guard but _edit_file_create still used getsize(): a FIFO stats as 0 bytes, fell into the zero-byte branch, and open() on a writerless pipe blocked the turn with no timeout and no cancel event. It also destroyed /dev/null under Full access.

3. A half-written emoji made the tool report itself as nonexistent. A truncated escape survives json.loads as a lone surrogate; _edit_file_write encodes on its first statement, outside every try, and the UnicodeEncodeError was swallowed upstream into Unknown tool: edit_file - the one answer that teaches the model this tool does not exist and sends it straight back to the whole-file rewrite this PR exists to eliminate. The swallow itself is pre-existing (python shows it too) and out of scope; the unguarded encode is PR code, so it is guarded there.

9 regression tests added. 6 of them fail against the unfixed source and pass with the fixes; suite is 53 passed.

Simulation

83 scenarios, 80 pass, plus 1500/1500 random edits byte-exact with 0 untruthful receipts. Groups: core replacement (8), encoding incl. BOM/non-UTF8/NUL/astral/UTF-16 (6), line endings (5), filesystem incl. suid/sticky/symlinks/traversal/hardlink/FIFO/socket/read-only dir/EXDEV (19), creation and clobber (6), concurrency (5), receipt truthfulness and bounds (12), arguments (9), size and memory (3), Full access (4), workdir shape (5).

The 3 failures are the two rejected items plus the hardlink case - all accepted limitations, none a regression.

Windows: the three landmines that would actually bite are handled - the mkstemp fd is closed before os.replace (a sharing violation otherwise), an empty old_string can never reach str.replace, and the BOM is stripped out of the matchable text. getattr(os, "O_NOFOLLOW", 0) degrades safely because O_EXCL still carries the no-clobber guarantee. os.replace surfaces a clean error on a Windows read-only destination rather than succeeding as POSIX does - safe either way, and the original survives with no temp file left behind.

On the rejections

Two are worth showing the numbers for, since both items are correct in the abstract:

• Mixed line endings: reproducible, but I measured prevalence before deciding - 3838 text files in this repo, 3788 pure LF, 0 pure CRLF, 6 mixed (0.16%), each a single stray line in a release-note fixture. The fix would restructure the write path used by the other 99.8%.
• Concurrent edits: 0 lost updates in 300 trials at 1 ms spacing and 0 at 50 and 500 ms, versus 74 of 300 when truly simultaneous. Two edit_file calls in a real session are separated by a model turn.

Not fixed, below the bar

The 200-char per-line cap can render a same-length edit past column 200 as identical -/+ lines; Created ... (N lines) is one too high for a file ending in a newline; the receipt shows a phantom trailing context line from split("\n"). All cosmetic - the bytes on disk are correct in every case. Also pre-existing and shared with python/terminal: _is_outside_workdir compares realpaths case-sensitively, which can reject a legitimate edit on a case-insensitive macOS or Windows volume.

CI

Repo tests (CPU) is pre-existing and flaky, not PR-caused: Backend CI is red on 17 of the 25 most recent main runs with no PR involved. The PR run's logs have expired (HTTP 410), so I substituted the local head-vs-base full-suite comparison above: identical real failures, +47 new passes.

Round update: one fix pushed, one rejected, plus the cross-platform read

65ee3f1c1 closes the only genuine defect this PR still shipped: on a full disk or over quota, creating a file left a truncated file that no later edit_file call could ever repair. Details are in the item threads; the short version is that it was reproduced with a real kernel write failure, not a mock, and the four new tests are discrimination-checked (3 of 4 fail against the reverted source, the fourth is the control).

Counts after the fix: tests/test_edit_file_tool.py 57 passed (53 existing + 4 new). A backend -k tool sweep gives 2594 passed / 5 failed / 10 errors against 2590 / 5 / 10 on the clean head, so exactly +4 and an identical failure set; every one of those failures is pre-existing and unrelated (needs a live server, a storage fixture, grandchild-process timing, or pymupdf). The PR's frontend tests are 16 passed, 0 failed.

Windows and macOS

• O_NOFOLLOW is correctly guarded with getattr(os, "O_NOFOLLOW", 0). It is absent on Windows and present on macOS, so nothing crashes anywhere; Windows simply gets no final-component symlink protection. Worth noting plain O_NOFOLLOW guards only the last component even on Linux and macOS, but the realpath containment check in _edit_file_resolve already covers the parents.
• os.replace is safe: the temp comes from tempfile.mkstemp(dir = directory), the destination's own directory, so it is never cross-filesystem. On Windows it maps to MoveFileExW(..., MOVEFILE_REPLACE_EXISTING) without MOVEFILE_COPY_ALLOWED, which is right for same-volume. The one behavioural difference: if the destination is held open by another process without FILE_SHARE_DELETE, the replace raises PermissionError, which is an OSError, so it is caught and returned as a clean Error: cannot write ... with the finally removing the temp. Degraded, not broken. Only POSIX rename documents atomicity; Windows does not.
• umask behaves as the docstring claims: os.open(target, flags, 0o666) gives 0o666 & ~umask, so 0644 under the usual 022, where mkstemp would have given 0600. That is exactly why the create path uses O_EXCL, and the unlink-on-failure fix preserves it.
• The new os.remove is Windows-safe: the with block has exited and CPython releases the descriptor even when the closing flush raises, so no open handle blocks the delete, and any residual failure is swallowed by contextlib.suppress(OSError).

Merging is otherwise safe. Nothing on the normal path is wrong, and the rejected item is not reachable on real input.

Merged current main in (8c4f6f618) rather than rebasing. This PR was CONFLICTING / DIRTY and 198 commits behind, so pre-commit.ci - pr was failing at the mergeable check rather than on any hook, and no other workflow could compute a merge ref.

One conflict, tool_loop_controller.py, additive on both sides: your edit_file branches in status_for_tool and awaiting_approval_status, and main's MCP display branches. Both kept, with the specific edit_file check ahead of the generic MCP lookup. Verified the merged behaviour directly rather than trusting the diff: status_for_tool("edit_file", {"path": "/a/b/notes.py"}) gives Editing: notes.py, awaiting_approval_status("edit_file") gives Waiting for approval: file edit, and the python and MCP paths still answer as before.

After the merge: tests/test_edit_file_tool.py 57 passed, tests/test_tool_loop_controller.py 23 passed. A wider -k sweep also surfaced 11 collection errors, all missing optional dependencies (fastmcp and friends) in unrelated modules that my filter pulled in whole; they reproduce without this branch.

One housekeeping note: the worktree had an out-of-band edit to studio/backend/utils/process_lifetime.py (a _signalable guard against a killpg(1) broadcast) whose own comment says it is superseded by the rebuild in #8797. It is unrelated to this PR's 11 files, so I kept it out of the merge rather than letting it ride along here.

Confirmed there is no file-editing tool in ALL_TOOLS today, so every agent edit goes through a whole-file rewrite, and this adds one that keeps the approval prompt and the workdir containment check. Will get this reviewed.

Codex Review: Didn't find any major issues. Hooray!

Reviewed commit: 07d8e1ff2c

@codex review

Codex Review: Didn't find any major issues. Swish!

Reviewed commit: ed9aeef3d3