fix(ui): make Share default to local download, Publish as opt-in (#481)

[Rchari1]

Fixes #481

Summary

The Share item in the chat overflow menu previously opened the public-link flow as the primary (and effectively default) action. Per #481 the expected default is a local download — exporting the conversation as a text file — with public-link creation as an explicit secondary opt-in.

Changes

• Message timeline overflow menu (message-timeline.tsx): add downloadSession() that serializes the session via serializeSession → Blob (text/markdown) and triggers a download (<a download> in the browser, save-file bridge in the VS Code webview). Make Download… the primary item (always enabled) and Publish… the secondary item (gated by shareEnabled, still opens the existing public-link popover).
• i18n (en.ts): add session.download.* keys.
• Save bridge (chat_bridge.ts): extend from PNG-only to *.md|*.txt|*.markdown|*.png, accepting data:text/markdown;base64, / data:text/plain;base64, in addition to data:image/png;base64,.

Verification

• pnpm -r run build + pnpm -r run typecheck pass
• packages/extension tests: 107 files, 1534 passed
• Manual: Share → downloads "<title>-<id>.md"; Publish still opens the public-link popover as a secondary action.

Intake was not-ready / suggested_path: B — user requested to proceed; this is the download-first fix.

Closes #481

Summary by CodeRabbit

• New Features
  • Added the ability to download session messages as Markdown.
  • Downloaded files use sanitized, session-specific filenames.
  • Downloads work in both the embedded app and standard browsers.
  • Added support for exporting Markdown and plain-text files alongside PNG images.
  • Added clear feedback for successful downloads and empty sessions.
• UI Updates
  • Updated session menu labels to use “Publish” terminology.

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

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Run ID: 21443f37-eb2d-4389-9b9e-682e3df0224b

📥 Commits

Reviewing files that changed from the base of the PR and between 3f3348a and dbeef49.

📒 Files selected for processing (4)

• packages/app-bundle/manifest.json
• packages/app-bundle/overlay/packages/app/src/i18n/en.ts
• packages/app-bundle/overlay/packages/app/src/pages/session/timeline/message-timeline.tsx
• packages/extension/src/chat_bridge.ts

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📝 Walkthrough

Walkthrough

The session timeline now exports messages as Markdown through browser or VS Code save paths. It adds download labels and empty-export feedback. The save bridge accepts PNG, Markdown, and text files with extension validation and type-specific save filters.

Changes

Session download

Layer / File(s)	Summary
Session export UI packages/app-bundle/overlay/packages/app/src/pages/session/timeline/message-timeline.tsx, packages/app-bundle/overlay/packages/app/src/i18n/en.ts, packages/app-bundle/manifest.json	The timeline serializes sessions, validates empty exports, creates sanitized filenames, exposes Download actions in both menus, updates share labels to Publish, adds localization strings, and refreshes bundle hashes.
Local save bridge packages/extension/src/chat_bridge.ts	The bridge accepts PNG, Markdown, and text data URLs, validates supported extensions, selects save filters, and writes decoded content.

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

Merge Risk: ⚪ Minimal · up to dbeef

Share now defaults to local Markdown download while public publishing remains an explicit opt-in, with the documented build, typecheck, test, and manual verification passing; no actionable merge-blocking risk remains.

Sequence Diagram(s)

sequenceDiagram
  participant User
  participant MessageTimeline
  participant serializeSession
  participant SaveBridge
  User->>MessageTimeline: Select Download
  MessageTimeline->>serializeSession: Serialize session messages
  MessageTimeline->>SaveBridge: Submit Markdown data URL
  SaveBridge-->>User: Open save dialog or browser download

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Suggested reviewers: aarontrowbridge

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the primary change: Share now downloads locally by default and Publish remains opt-in.
Linked Issues check	✅ Passed	The changes satisfy issue #481 by making local Markdown download the default and keeping public-link publishing as an explicit secondary action.
Out of Scope Changes check	✅ Passed	The localization, serialization, save-bridge, menu, and manifest changes directly support the download-first sharing behavior.
Docstring Coverage	✅ Passed	Docstring check was indeterminate for this PR — some files could not be analyzed in time. Not blocking.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/481-share-download-first

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