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

scripts/brain/src/scaffold.ts

@@ -0,0 +1,117 @@
+/**
+ * `initBrain` — the idempotent runtime scaffold for the second brain (SB-S0 D1/D5).
+ *
+ * Creates the `brain/` + `ingest/` tree under the per-user data dir (via the
+ * `dataRoot` resolver, so `LINKEDIN_STUDIO_DATA` relocates it for tests + real
+ * installs). Idempotent + migration-safe: a directory that exists is left alone,
+ * a file that exists is NEVER rewritten (compare-then-skip, never blind-write) —
+ * so a second run is a no-op and a user-edited file is preserved.
+ *
+ * NO session-start wiring (SB-S2 owns that) — this only ships the invokable init.
+ */
+
+import { existsSync, mkdirSync, readFileSync, writeFileSync } from "node:fs";
+import { dirname, join } from "node:path";
+import { fileURLToPath } from "node:url";
+
+import { dataRoot } from "./dataRoot.js";
+import { foldUserProfile, serializeProfile } from "./profile.js";
+
+const HERE = dirname(fileURLToPath(import.meta.url));
+/** The shipped template that defines the canonical profile field-set. */
+const TEMPLATE_PATH = join(HERE, "..", "..", "..", "config", "user-profile.template.md");
+/** The runtime instance (if the user copied + filled the template). */
+const INSTANCE_SUB = join("profile", "user-profile.md");
+
+const SCAFFOLD_DIRS = ["brain/journal", "ingest/inbox", "ingest/published"];
+
+function today(): string {
+  return new Date().toISOString().slice(0, 10);
+}
+
+function indexSeed(): string {
+  return `# Brain — Index (MOC)
+
+> Map of Content — one screen pointing at every tributary, with a freshness flag.
+> Generated by \`brain init\`; safe to hand-edit (a re-run never clobbers it).
+
+| Tributary | What it holds | Freshness |
+|-----------|---------------|-----------|
+| voice-samples | writing style | — |
+| specifics-bank | lived raw material | — |
+| trends | external signal | — |
+| analytics | performance | — |
+| ingest | inbox + published (the gold signal) | — |
+
+- [profile.md](profile.md) — semantic, two-layer (static + dynamic) profile
+- [operations.md](operations.md) — plans · ideas · the "who I am now" anchor
+- journal/ — episodic, append-only session log (the consolidation loop's source)
+`;
+}
+
+function operationsSeed(): string {
+  return `# Operations
+
+## Who I am now (anchor)
+
+<!-- Frozen-past-self guard: a periodic, user-authored "where I'm headed now"
+     statement that deprecates older inferences. Update it when your direction shifts. -->
+
+## Plans
+
+## Ideas
+`;
+}
+
+function profileSeed(): string {
+  const templateText = readFileSync(TEMPLATE_PATH, "utf8");
+  const instancePath = dataRoot(INSTANCE_SUB);
+  const instanceText = existsSync(instancePath) ? readFileSync(instancePath, "utf8") : undefined;
+  return serializeProfile(foldUserProfile({ templateText, instanceText, today: today() }));
+}
+
+export interface InitResult {
+  /** Data-relative paths created this run. */
+  created: string[];
+  /** Data-relative paths that already existed and were left untouched. */
+  skipped: string[];
+}
+
+/**
+ * Create the brain scaffold idempotently. Returns the created/skipped split.
+ * File content seeds are computed lazily, so an already-present file costs no
+ * template read or fold.
+ */
+export function initBrain(): InitResult {
+  const created: string[] = [];
+  const skipped: string[] = [];
+
+  for (const sub of SCAFFOLD_DIRS) {
+    const abs = dataRoot(sub);
+    if (existsSync(abs)) {
+      skipped.push(sub);
+    } else {
+      mkdirSync(abs, { recursive: true });
+      created.push(sub);
+    }
+  }
+
+  const files: Array<{ sub: string; seed: () => string }> = [
+    { sub: "brain/profile.md", seed: profileSeed },
+    { sub: "brain/index.md", seed: indexSeed },
+    { sub: "brain/operations.md", seed: operationsSeed },
+  ];
+
+  for (const { sub, seed } of files) {
+    const abs = dataRoot(sub);
+    if (existsSync(abs)) {
+      skipped.push(sub);
+      continue;
+    }
+    mkdirSync(dirname(abs), { recursive: true });
+    writeFileSync(abs, seed(), "utf8");
+    created.push(sub);
+  }
+
+  return { created, skipped };
+}