WIP: Loom -> Cap importer (#363)

apps/chrome-extension/docs/loom-import-plan.md

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+# Loom -> Cap importer (issue #363)
+
+## Existing pieces this reuses
+- `apps/chrome-extension/src/shared/api.ts` — extension already has a full
+  auth flow (`createAuthStart` / `parseAuthResponse` via `chrome.identity`,
+  bearer-token requests against `/api/extension/...`). The importer reuses
+  this instead of inventing a second auth path.
+- `apps/web/app/api/tools/loom-download/route.ts` — already resolves a Loom
+  video id to a direct/streaming CDN url and can transcode it. The importer
+  backend route reuses `tryGetDirectMp4Url`-equivalent logic instead of
+  reimplementing Loom CDN resolution.
+- `Extension.ExtensionApiPaths` in `@cap/web-domain` — the extension/web
+  contract lives here; new paths must be added to this shared schema so
+  drift fails to compile (per existing pattern in `shared/api.ts`).
+
+## New pieces needed
+1. `Extension.ExtensionApiPaths` additions: `listLoomSpaces`,
+   `listLoomVideos`, `importLoomVideos`.
+2. `apps/web/app/api/extension/[...route]/loom-importer.ts` (new): given the
+   user's Loom session (read client-side, see below), returns spaces + videos
+   for the signed-in user, and a POST endpoint that, for each selected video
+   id, resolves the CDN url (reusing `loom-download`'s resolver) and creates
+   a Cap video record tagged with `loomVideoId`.
+3. Schema: `videos` table needs a nullable `loomVideoId` column
+   (`packages/database`) + migration, so re-imports are idempotent.
+4. Extension UI: new page (`import-loom.html` + `src/import-loom/main.tsx`,
+   following the `options` page pattern) — user picks a space, sees a
+   preview list, confirms import.
+5. Loom space/video listing: Loom has no public read API for third parties.
+   Plan is to read it from the user's own loom.com session via a content
+   script injected on `loom.com/*` (`host_permissions` already broad enough),
+   posting the space/video list back to the background service worker —
+   mirrors how the recorder overlay talks to the service worker today.
+
+## Open questions for maintainers (to ask on the PR)
+- Preferred destination for a brand-new Cap space vs. only existing spaces on
+  first version (issue text allows both; starting with "existing spaces
+  only" keeps the first PR small).
+- Whether `loomVideoId` should be unique per user or per workspace (affects
+  the idempotency migration).
+
+## Status
+Scaffolding + plan only. Auth wiring, backend route, migration and UI still
+to be implemented in follow-up commits on this branch.