feat(linkedin-studio): second-brain SB-S0 foundation — brain/ scaffold + profile fold + id/provenance spine [skip-docs]

SB-S0 (Foundation) of the second-brain arc: a new TS package scripts/brain/
(structural copy of specifics-bank) establishing the spine later slices hang on.
TDD throughout (failing test first); fold scope = P1+P2 only per operator decision.

- types.ts: one provenance vocab (human|published|ai-draft) + the six-field
  ProfileFact record + two-layer ProfileDoc.
- id.ts: slugify + mintEntityId (sha256[:12], kind-namespaced, slug-keyed so the
  id is stable across value edits) + normalizeProvenance (throws on unknown). [SC4]
- profile.ts: no-YAML line-grammar parse/serialize (parse∘serialize = identity over
  the whole doc; values may contain ]/|/quotes) [SC2] + foldUserProfile: lossless,
  idempotent, source-absent-aware fold of config/user-profile.template.md. Pinned
  extraction — P1 labeled scalars (group-headers skipped, [placeholder]→empty) + P2
  expertise group; stops at "### Research Tooling" so deferred explainer prose can't
  leak in as fields. Checkbox-prefs (Goals/Tone/MCPs/Assets) deferred (§8). [SC3]
- dataRoot.ts: inline per-package resolver (repo idiom; no new seam → SC6).
- scaffold.ts/cli.ts: idempotent `brain init` — brain/{index,profile,operations}.md
  + journal/ + ingest/{inbox,published} under the data-dir; compare-then-skip, never
  clobbers a user edit. No session-start wiring (SB-S2 owns it). [SC1]

Gate: new BRAIN floor in test-runner.sh (34 tests; trends/specifics/contract floors
unchanged) + anti-erosion floor 74→75. Full gate 90/0/0, tsc --noEmit clean. [SC5/SC6]
No new command/agent/reference → no version bump, no structure-count change.

Refs docs/second-brain/{brief,plan-sb-s0,architecture}.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RigJBiRFNtFZKCz21qNbQ4

docs/second-brain/architecture.md

@@ -1,6 +1,6 @@
 # Second Brain — Architecture Design
 
-> **Status:** architecture **approved by operator 2026-06-23**. Design phase — no code yet.
+> **Status:** architecture **approved by operator 2026-06-23**. **SB-S0 (Foundation) landed 2026-06-23** (`scripts/brain/`, 34 tests, gate-wired); S1–S4 remain design-phase.
 > **Boundary (confirmed 2026-06-23):** the **engine** (store schema · evolution loop · ingest seam) → **the plugin** (domain-general, shareable); the **user's data** (posts · articles · newsletters · plans · ideas) → the **per-user data dir** (`${LINKEDIN_STUDIO_DATA:-$HOME/.claude/linkedin-studio}/`, survives reinstall); the **personal cockpit** (the operator's day-to-day operations centre) → **Maskinrommet** (a thin layer that reads/writes *through* the plugin's store, never a fork of the engine).
 > **Research inputs (three parallel threads, 2026-06-23):** `research/connector-egress.md` · `research/secondbrain-sota.md` · `research/silo-inventory.md`.
 
@@ -74,7 +74,7 @@ Run on a cadence (reuse the existing session-start staleness-nudge surface) as a
 
 | Slice | Content | Why this order |
 |-------|---------|----------------|
-| **SB-S0 — Foundation** | `brain/` scaffold + two-layer `profile.md` (fold in `user-profile.md`) + `index.md` MOC + `operations.md` + `journal/`; entity-id + provenance shape as a small typed, tested module; `ingest/` dirs + manual-import contract. **No loop yet.** | Smallest thing that stands up and is testable; locks the id/provenance spine everything hangs on |
+| **SB-S0 — Foundation** ✅ *landed 2026-06-23* | `brain/` scaffold + two-layer `profile.md` (fold in `user-profile.md`) + `index.md` MOC + `operations.md` + `journal/`; entity-id + provenance shape as a small typed, tested module; `ingest/` dirs + manual-import contract. **No loop yet.** Shipped as `scripts/brain/` (TS, 34 tests, gate-wired BRAIN floor); fold = P1 labeled-scalars + P2 expertise (checkbox-prefs deferred, §8 of `plan-sb-s0.md`). | Smallest thing that stands up and is testable; locks the id/provenance spine everything hangs on |
 | **SB-S1 — Ingest + gold signal** | Manual import → `ingest/published/` with `provenance=published`; wire profile/voice to learn from published-only | The gold signal before the loop that consumes it |
 | **SB-S2 — Evolution loop** | Sleep-time consolidation (reuse session-start surface): journal+published+tributary deltas → profile **diff** w/ evidence_count/provenance/timestamps; threshold promotion; contradiction reconciliation; brain-wide freshness nudge | The compounding mechanism |
 | **SB-S3 — Cross-silo graph + ops centre** | Thread the id through tributaries (post↔specific↔trend↔analytics assemblable); flesh out `operations.md`; retire the dead `content-history.md` + triple-post reconciliation | Finally answers "which raw material performs?" |