# Background-job output appears inside an open file

An open bug, not reproducible on demand, with a trap already set for it. **If someone has just reported
this, skip to "When it is reported".**

Status as of 2026-08-16: cause unknown, two candidates eliminated, instrumentation shipped.

## What it looks like

A file is open in the code editor while a background job is producing output — a dev server, a watcher.
The output appears **inside the file's buffer**, spliced into the middle of it. Observed once with a
`bun dev` job: the JSX of `SigninScreen.tsx` and eight lines of dotenv/POSTGRES_URL output shared the
buffer, with Monaco's line numbers continuing straight through (…180, the log lines, then 189 `</Link>`).

Two details from that report do most of the diagnostic work:

- **The tab was marked dirty.** So the model really was mutated; this is not a rendering artefact.
- **The file on disk was untouched.** The corruption is in the browser and was never saved. Reopening the
  tab fixes it.

## What has been ruled out, and why

Do not re-investigate these without new evidence.

| Candidate                                                | Why it is out                                                                                                                                                                       |
| -------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| The end-of-turn refresh re-reading the file              | `reloadFile` sets `originalContent` and `isDirty: false`. It cannot produce a dirty tab.                                                                                            |
| A shared component between the task panel and the editor | `CodeSurface` (the task log) renders with shiki. It is not Monaco and holds no editor model.                                                                                        |
| Two Monaco editors sharing a model                       | The app's only other mount, `FileViewer/renderers/EditorRenderer.tsx`, passes no `path`, so its model URI is `inmemory://model/N` and cannot collide with the editor's `file:///…`. |
| Something typing into the page                           | No `execCommand('insertText')`, no synthesised `KeyboardEvent`, no clipboard writes anywhere near the editor.                                                                       |

That leaves **Monaco's own `onChange`** — the model was edited the way a paste or a programmatic
`executeEdits` edits it. Which is why this needs to be caught in the act rather than reasoned about.

One thing to check first, because it is recent and it is ours: `2b70a570` gave `<Editor>` a real `path`,
so models are keyed by file URI globally rather than per mount. Two panels open on the same file now share
one model. That should be an improvement, and it is a change in exactly the layer that turns out to be
involved.

## When it is reported

Ask for one thing. In the browser's console, on the machine where it happened:

```js
JSON.parse(localStorage.getItem('officer:editor-buffer-trap'));
```

That returns up to the last five occurrences, each with:

| Field              | What it tells you                                                                                     |
| ------------------ | ----------------------------------------------------------------------------------------------------- |
| `stack`            | **The answer.** The call stack at the moment of the edit — whatever inserted the text is named in it. |
| `inserted`         | The first 200 characters that arrived. Confirms it is job output rather than a real paste.            |
| `charactersAdded`  | How much arrived at once.                                                                             |
| `path`             | Which file was open.                                                                                  |
| `at`               | Lines it up against the job's own logs.                                                               |
| `editorWasFocused` | Always `false` — the trap only fires when it is.                                                      |

It is written by `reportSuspiciousEdit` in `apps/CodeEditor/CodeEditor.tsx`, which fires on any insertion
over 200 characters arriving while the editor does **not** have focus. Nobody types 200 characters into an
editor they are not focused on.

If the key is empty but the corruption happened, that is itself informative: either the editor **was**
focused (so it plausibly is a paste, and the question becomes what pasted it), or the insertion arrived in
chunks under 200 characters — in which case lower `SUSPICIOUS_INSERT` and wait for it again.

## Why a trap rather than a fix

Because every fix available without knowing the cause is a guess that would look like a solution. A guard
that refuses suspicious writes would hide the symptom on the one screen where it is visible, and the same
mechanism would go on doing whatever else it does. The corruption is never saved and reopening the tab
clears it, so the cost of waiting is low and the cost of a wrong fix is a bug that stops being reportable.

## When it is solved

Delete all of it: `reportSuspiciousEdit`, `EDITOR_TRAP_KEY`, its call in the `onChange` handler, the entry
in `TODO.md` → Known bugs, and this file. It is instrumentation for one bug, and instrumentation nobody
remembers the reason for is worse than none.