test(brain): fake-CLI agent-obedience E2E for /office-hours writeback

test/skill-e2e-office-hours-brain-writeback.test.ts (~210 LOC,
periodic-tier, ~$0.50-1/run):

Drives /office-hours via runSkillTest against a deterministic fixture
brief (pixel.fund founder pitch). The workdir has:
  - A regenerated office-hours/SKILL.md with the compressed brain blocks
    (generated via gen-skill-docs --respect-detection against a temp
    GSTACK_HOME, then restored to canonical post-snapshot)
  - A fake gbrain shell script on PATH that uses printf %q quoting to
    preserve --content "$(cat <<'EOF' ... EOF)" heredoc payloads
    intact (naive `echo "$@"` would lose argv boundaries)
  - The docs/gbrain-write-surfaces.md the resolver points to

Asserts:
  - gbrain-calls.log contains `gbrain put office-hours/pixel-fund`
  - Payload file at gbrain-payloads/office-hours/pixel-fund.md exists
    with valid YAML frontmatter (title: + tags: + design-doc tag)
  - At least one gbrain put entities/<name> call (entity stub
    enrichment is best-effort, soft warning if absent)

Covers agent obedience to the SAVE_RESULTS instruction. Out of scope:
gbrain CLI persistence contract (T11 covers that with real PGLite).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/fixtures/office-hours-brain-writeback/brief.md

@@ -0,0 +1,30 @@
+# Founder pitch — pixel.fund
+
+Founder: Maya Chen (CEO, ex-Stripe), co-founder Aria Patel (CTO,
+ex-Robinhood). YC W26.
+
+## What
+
+A donation-budget tool for solo creators. Set a monthly $ floor for
+causes you care about, pixel.fund auto-allocates each dollar across your
+chosen orgs (Direct Relief, GiveDirectly, etc.) the moment a Stripe
+payout lands. One-line embeddable receipt. 1% platform fee.
+
+## Traction
+
+- 2026-04-01 launched private beta with 14 creators from her newsletter
+- 2026-05-15 hit 51 paying creators, $4,200 MRR
+- Waitlist of 230 from a single tweet by a tech-Twitter influencer
+- Two creators asked about a "team plan" (multi-seat) unprompted
+
+## Status quo
+
+Creators today either (a) write checks ad-hoc and forget about it, or
+(b) use Patreon-style platforms where the "cause" is opaque (general
+fund). Maya talked to 40 creators in YC interviews — 31 said they "want
+to give more but it's mental overhead."
+
+## What Maya wants from office hours
+
+Should she chase the team-plan signal, or go deeper on the solo flow
+first? She's two weeks from running out of YC dorm food.