Add per-block auto save option to the editor

[NGdev2]

Summary

Adds an optional auto-save to the file editor, as requested in #1080. Saving is manual today (Ctrl+S / Save button), which is easy to forget when editing a file next to a preview or terminal.

(Asked about this in #ideas on Discord before opening.)

Changes

• Menu (preview-model.tsx): a new "Auto Save" submenu in the editor's settings menu (gear icon), right under Word Wrap:
  • Off (default, no behavior change)
  • After Delay: saves 1s after typing pauses; each edit restarts the timer
  • On Focus Change: saves when the block loses focus (e.g. clicking into a terminal)
• Storage: the choice is stored per block as the editor:autosave meta key, set with SetMetaCommand like the font size menu. New key added in pkg/waveobj/wtypemeta.go; metaconsts.go and gotypes.d.ts regenerated.
• Auto-save logic (preview-edit.tsx): two effects on the code editor. Read-only files are never auto-saved.
• Save fix (preview-model.tsx): handleFileSave now only clears newFileContent if nothing was typed while the write was in flight. Before, edits made during a save were treated as saved and could be lost. Rare with manual saves, but auto-save can save mid-typing.

Test plan

• After Delay: type, the file saves ~1s after typing stops (checked with cat, and with a preview block of the same file, which updates on its own when combined with Auto-refresh file preview when the file changes on disk #3547)
• After Delay: typing continuously doesn't save until a pause, no characters lost
• On Focus Change: type, click into another block, the file saves
• Off: nothing saves automatically
• prettier passes, Go builds, tsc reports no new errors

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ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Repository UI
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📥 Commits

Reviewing files that changed from the base of the PR and between e7da2ba and 030194f.

📒 Files selected for processing (1)

• frontend/app/view/preview/preview-model.tsx

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Walkthrough

The preview editor adds Off, After Delay, and On Focus Change autosave modes. It reads and stores the selected mode in block metadata. Delayed autosave waits 1,000 ms after content changes, while focus-change autosave saves when the editor loses focus. File writes run serially. After a successful write, pending content is cleared only when it still matches the written content.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 03019

The previously identified risk of an older autosave overwriting newer edits is addressed. No actionable merge-blocking risk remains from the supplied evidence.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description clearly explains the per-block auto-save options, storage metadata, save behavior, and test plan. It directly matches the changeset.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding a per-block auto-save option to the editor.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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Inline comments:
Review comments at @frontend/app/view/preview/preview-edit.tsx:
- Line 59: Update the autosave flow around handleFileSave so a timer firing
while a save for the same file is pending cannot start a competing write or let
a stale completion clear the latest edit. Serialize saves per file, or reject
stale completions while retaining the latest content for a subsequent save.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: Repository UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: 12a4eaa9-f5ce-4c8a-b5ff-c326f044ef49

📥 Commits

Reviewing files that changed from the base of the PR and between 9f1c967 and e7da2ba.

📒 Files selected for processing (5)

• frontend/app/view/preview/preview-edit.tsx
• frontend/app/view/preview/preview-model.tsx
• frontend/types/gotypes.d.ts
• pkg/waveobj/metaconsts.go
• pkg/waveobj/wtypemeta.go

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 8 remain after this review.