Summary

PR 1 of 7 in the Session Library redesign. Pure data-layer change with no UI changes.

• Adds cross-source project identity computation: git_remote → git_common_dir → manifest_path → loose → path (short-circuit priority)
• Migrates DB to user_version 6: identity_kind / identity_key columns on projects + index, plus project_groups_v view that aggregates same-identity rows across sources
• Backfills existing rows on migration (idempotent, transactional)
• New listProjectGroups() query for upcoming UI consumption
• Identity-derived display name falls back to existing resolveProject name for new sessions

Spec & plan

• Spec: ~/Documents/dev-docs/spool/session-library.md §4
• Plan: ~/Documents/dev-docs/spool/plans/session-library-pr1.md
• Master PR sequence: ~/Documents/dev-docs/spool/plans/session-library.md

Files changed

packages/core/src/projects/
  identity.ts          158  (5-step priority, IdentityFs DI)
  identity.test.ts     114  (10 cases incl. worktree + null-cwd loose)
  display-name.ts        6
  display-name.test.ts  18
  groups.ts             29  (listProjectGroups)
  groups.test.ts        54
  fs.ts                 14  (realFs adapter, 5s spawn timeout)
  e2e.test.ts           45  (cross-source unification)
packages/core/src/db/
  db.ts                +55  (v6 migration + backfillProjectIdentities)
  migration-v6.test.ts  79  (5 cases incl. backfill)
  migration-v5.test.ts  ±6  (assertion adapt)
  queries.ts            ±7  (signature + identity persistence)
  queries.test.ts       34  (identity persistence)
  stars.test.ts         +1  (caller adaptation)
packages/core/src/sync/
  syncer.ts             ±9  (computeIdentity wired in)
packages/core/src/types.ts +22  (ProjectIdentity, ProjectGroup types)

11 commits, ~640 LOC net. Logical units: types → identity computation → display name util → migration v6 → query persistence → syncer wiring → backfill → groups query → e2e test → strict-tsc fix → final fixes (spawn timeout + portable test).

Test plan

• pnpm --filter @spool-lab/core test — 73 passed (15 test files)
• pnpm --filter @spool-lab/core build — clean
• Full workspace pnpm build (Turbo, 3 packages) — clean
• Existing v5 migration test still passes
• Existing stars test still passes
• Existing syncer test passes un-touched (cwd /tmp/... short-circuits to loose, no real git spawn)

Noteworthy / deferred

• getOrCreateProject does not refresh display_name on existing rows. Pre-existing pattern; identity columns are correctly set on insert. If a project's package.json name field changes after first index, the display name stays stale. Future PR can add ON CONFLICT DO UPDATE.
• listProjectGroups not yet exported from index.ts. Intentional — UI consumes it in PR 3 (Library Shell + Sidebar). Public surface stays unchanged.
• spawnSync has a 5s timeout. Mirrors the fix already applied in Spool Daemon to prevent hung git config calls (slow ssh-agent, network mounts) from blocking indexing.
• Spec deviation (cosmetic): view uses MIN(p.display_name) not COALESCE(MIN(display_name), MIN(slug)). Equivalent in practice — display_name is NOT NULL.

What this PR does NOT do

Per the master PR sequence:

• No sidebar / project list UI (PR 3)
• No Star UI hide (PR 2)
• No Pin (PR 5)
• No search migration (PR 6)
• No session detail integration (PR 7)
• No DESIGN.md changes (PR 3)

The new project_groups_v view is built but unused by the UI — by design.