fix(editor): scope external disk syncs and encoding reloads to one model

[wgqqqqq]

Summary

Follow-up to #3185. Two dirty-state correctness gaps around programmatic disk writes in the code editor.

1. Root cause: external-sync suppression was process-wide. MonacoModelManager tracked it with a global depth counter, so a bracketed disk write on one model also muted dirty tracking for every other model that a content listener edited synchronously during that write. The bracket is now tracked per model (WeakMap), and a disk write still emits monaco-model-content-changed while dirty tracking is suppressed.

2. Root cause: the encoding reload had no request ownership. handleEncodingConfirm awaited readFileContent and then wrote the result unconditionally, so a slow read could overwrite a newer view, a newer encoding selection, or edits made while the read was in flight. It now guards on a request id, a live model/view check, and the model's alternative version id, and commits the decoded buffer together with its saved baseline (applyDiskSnapshotToEditor) before awaiting file metadata.

Follow-up to #3185, related to #3165.

Type and Areas

Type: regression fix

Areas: web UI (src/web-ui/src/tools/editor)

Motivation / Impact

The global counter made the #3165 fix too broad: any model edited by a content listener while another model was being synced from disk silently skipped its dirty recompute and its dirty-state broadcast, so a tab could keep showing a stale modified/unmodified state. Scoping the bracket to the synchronized model keeps the original guarantee - no transient "modified" flash for a disk sync - without suppressing unrelated edits.

The encoding reload guard closes a race where a slow read resolved after the user had switched view, picked another encoding, or typed; the resolved content then replaced newer state. No user-facing strings change.

Verification

• pnpm --dir src/web-ui run test:run src/tools/editor/components/CodeEditor.test.tsx src/tools/editor/services/MonacoModelManager.test.ts src/tools/editor/services/EditorDocument.test.ts src/tools/editor/utils/diskFileVersion.test.ts -> 4 files, 39 tests passed
• pnpm run type-check:web -> passed
• node scripts/check-git-object-sizes.mjs --base upstream/main --head HEAD -> no unapproved objects

Not covered by these checks: live SSH and peer-device transport for the editor, and manual interaction in a running editor.

Reviewer Notes

• Prepared with AI assistance in a worktree; testing level: focused tests plus type-check, not manually exercised in a running editor.
• The new CodeEditor.test.tsx renders the real CodeEditor against the real MonacoModelManager and EditorDocument, with fake Monaco rendering and host IO. It covers delayed reads, stale requests, surface changes, and view remounts.
• The branch is one commit on top of 0be594d8b (current upstream/main), so the PR diff is only that commit.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable.

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