feat(extension): save useful posts (Phase 1)

[erichuang1425]

Summary

First, merged the one outstanding unmerged PR (#8, "new posts since last visit") — its lone review comment was already resolved and CI was green, so it merged cleanly into main. Then continued Phase 1 with the next roadmap item: save comments.

ForumForge now lets the reader save any useful post from a thread. Each post gets a Save / Saved toggle in the side panel; saving keeps an on-device snapshot (the post content frozen at save time) plus where it came from, so the saved item stays stable even if the page later changes — and can be revisited and exported to Markdown later (the next Phase 1 item).

Everything stays on-device (local-first, see docs/PRIVACY.md): nothing about what you keep leaves the browser, and no new permissions are needed — saved posts reuse the existing storage permission.

click Save ─▶ post id → frozen snapshot ─▶ key by thread ─▶ persist ─▶ reflect "Saved"

What changed

• src/savedPosts.ts (new) — a SavedPosts store over a @forumforge/storage Collection. A SavedPost is a frozen snapshot plus provenance (thread key, page URL, title, savedAt). Keys are namespaced per thread (<threadKey> <postId>), so the same post id in two different threads can't collide; the thread key reuses readHistory's fragment-normalization so a post anchor in the URL doesn't fork the key. API: save / remove / isSaved / toggle / savedIdsFor / all.
• src/render.ts — each post gets a Save/Saved toggle reflecting options.savedPostIds. The state is carried by the label and aria-pressed (not color alone). renderThread stays a pure view; setSaveButtonState is exported and shared by initial render and the panel's click update so the two never drift.
• src/sidepanel.ts — loads the thread's saved ids, passes them to render, and a single delegated click handler (on the persistent output container) toggles save state against the frozen post snapshot. The button reflects what storage actually reached — a failed write leaves the label honest.
• public/sidepanel.html — Save toggle styles (pill button, pressed state).

Docs synced in the same change: ROADMAP.md, the canonical Initial Plan.md checklist, and the extension README.md.

Roadmap (Phase 1)

• Clean reading mode
• OP highlighting
• New posts since last visit
• Save comments ← this PR
• Local user notes
• Markdown export
• Discourse adapter
• Hacker News adapter

Verification

• pnpm -r typecheck — passes (core + parser + storage + extension)
• pnpm test — 102 tests pass (+12: saved-post store, per-thread key namespacing, Save rendering & state toggling)
• pnpm --filter @forumforge/extension build — bundles dist/

Intentionally not done

• A saved-posts list / management view and Markdown export — SavedPosts.all() already returns saved posts most-recent-first to feed it, but the UI and export are the next Phase 1 items, out of scope here.
• Clicking through in a real browser is a manual step (needs a browser); the store, render, and wiring are unit-tested.

🤖 Generated with Claude Code

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