feat(brain): wire 5 planning skill templates with BRAIN_* placeholders (T6)

Adds three placeholders to each of the 5 planning SKILL.md.tmpl files:
  {{BRAIN_PREFLIGHT}}     — top of skill body, before first interactive
                            section. Loads the per-skill digest subset
                            (5 files for office-hours, 2 for plan-eng-
                            review, etc.) into the prompt context before
                            any AskUserQuestion fires.
  {{BRAIN_WRITE_BACK}}    — end of skill, before refresh hook. Phase 2
                            calibration write path; gated on personal
                            policy + BRAIN_CALIBRATION_WRITEBACK flag.
  {{BRAIN_CACHE_REFRESH}} — end of skill, after write-back. Non-blocking
                            background refresh so next invocation gets
                            warm cache.

Files touched (templates + regenerated SKILL.md):
  office-hours/SKILL.md.tmpl
  plan-ceo-review/SKILL.md.tmpl
  plan-eng-review/SKILL.md.tmpl
  plan-design-review/SKILL.md.tmpl
  plan-devex-review/SKILL.md.tmpl
  (matching .md files regenerated via bun run gen:skill-docs)

All 5 generated SKILL.md files now contain the rendered ## Brain Context
(preflight) section + write-back guidance + background-refresh hook. The
resolver renders only for skills in SKILL_DIGEST_SUBSETS — these 5 + an
empty string for any other skill that drops in the placeholders.

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

office-hours/SKILL.md

@@ -770,6 +770,44 @@ You are a **YC office hours partner**. Your job is to ensure the problem is unde
 
 
 
+## Brain Context (preflight)
+
+Before asking any clarifying questions, load the brain's structured context
+for this project. The cache layer handles staleness, refresh, and stale-but-
+usable fallback automatically. Skip questions whose answers are already
+present in the loaded context; ground recommendations in what the brain
+already knows about the user, the product, the goals, and recent decisions.
+
+```bash
+eval "$(~/.claude/skills/gstack/bin/gstack-slug 2>/dev/null)" 2>/dev/null || true
+{
+  printf '## Brain Context\n\n'
+  printf '\n### %s\n\n' "product"
+  ~/.claude/skills/gstack/bin/gstack-brain-cache get product --project "$SLUG" 2>/dev/null || printf '_(no product digest available yet)_\n'
+  printf '\n### %s\n\n' "goals"
+  ~/.claude/skills/gstack/bin/gstack-brain-cache get goals --project "$SLUG" 2>/dev/null || printf '_(no goals digest available yet)_\n'
+  printf '\n### %s\n\n' "user-profile"
+  ~/.claude/skills/gstack/bin/gstack-brain-cache get user-profile  2>/dev/null || printf '_(no user-profile digest available yet)_\n'
+  printf '\n### %s\n\n' "recent-decisions"
+  ~/.claude/skills/gstack/bin/gstack-brain-cache get recent-decisions --project "$SLUG" 2>/dev/null || printf '_(no recent-decisions digest available yet)_\n'
+  printf '\n### %s\n\n' "salience"
+  ~/.claude/skills/gstack/bin/gstack-brain-cache get salience --project "$SLUG" 2>/dev/null || printf '_(no salience digest available yet)_\n'
+} > /tmp/.gstack-brain-context-$$.md 2>/dev/null
+[ -s /tmp/.gstack-brain-context-$$.md ] && cat /tmp/.gstack-brain-context-$$.md
+rm -f /tmp/.gstack-brain-context-$$.md 2>/dev/null || true
+```
+
+**How to use this context:**
+- If `product` digest names the value prop, target user, or stage — don't re-ask.
+- If `goals` digest lists active goals — frame recommendations against them.
+- If `recent-decisions` digest names a prior scope/architecture choice — flag if this plan contradicts.
+- If `user-profile` digest carries calibration pattern statements ("tends to over-engineer security") — surface them when relevant.
+- If a digest is `(no X digest available yet)`, treat that section as cold; ask the user.
+
+**Privacy:** Salience digest is filtered by allowlist (D9 default: `projects/`,
+`gstack/`, `concepts/` only). Personal/family/therapy content never leaks here.
+
+
 ## Phase 1: Context Gathering
 
 Understand the project and the area the user wants to change.
@@ -1703,6 +1741,59 @@ Present the reviewed design doc to the user via AskUserQuestion:
 
 
 
+## Brain Calibration Write-Back (Phase 2 / gated)
+
+When the skill makes a typed prediction worth tracking (scope decision,
+TTHW target, architectural bet, wedge commitment), it MAY write a
+`kind=bet` take to the brain so a calibration profile builds over time.
+
+**Gated on two things:**
+1. Brain trust policy for the active endpoint is `personal` (check via
+   `~/.claude/skills/gstack/bin/gstack-config get brain_trust_policy@<endpoint-hash>`).
+   Shared brains skip write-back to avoid polluting team calibration.
+2. Feature flag `BRAIN_CALIBRATION_WRITEBACK` is set (today: false; flips
+   to true when upstream gbrain v0.42+ ships `takes_add` MCP op).
+
+When both gates pass, the write-back path uses `mcp__gbrain__takes_add`
+to record a take with weight 0.9 (per SKILL_CALIBRATION_WEIGHTS).
+If the MCP op is unavailable, fall back to `mcp__gbrain__put_page` with
+a gstack:takes fence block (documented but uglier path).
+
+Mandatory take frontmatter shape:
+```yaml
+kind: bet
+holder: <user identity from whoami>
+claim: <one-line prediction the skill is making>
+weight: 0.9
+since_date: <today's date>
+expected_resolution: <date in 1-3 months depending on skill>
+source_skill: office-hours
+```
+
+After write, invalidate the affected digests so the next preflight reflects
+the new state:
+
+```bash
+eval "$(~/.claude/skills/gstack/bin/gstack-slug 2>/dev/null)" 2>/dev/null || true
+  ~/.claude/skills/gstack/bin/gstack-brain-cache invalidate product --project "$SLUG" 2>/dev/null || true
+  ~/.claude/skills/gstack/bin/gstack-brain-cache invalidate goals --project "$SLUG" 2>/dev/null || true
+  ~/.claude/skills/gstack/bin/gstack-brain-cache invalidate competitive-intel --project "$SLUG" 2>/dev/null || true
+```
+
+
+## Brain Cache Background Refresh
+
+After the skill's work completes (and telemetry has logged), kick a
+background refresh of any cache digest that's getting close to its TTL.
+This is non-blocking — the user doesn't wait. Next invocation benefits
+from the warm cache.
+
+```bash
+eval "$(~/.claude/skills/gstack/bin/gstack-slug 2>/dev/null)" 2>/dev/null || true
+(~/.claude/skills/gstack/bin/gstack-brain-cache refresh --project "$SLUG" 2>/dev/null &) || true
+```
+
+
 ---
 
 ## Phase 6: Handoff — The Relationship Closing

office-hours/SKILL.md.tmpl

@@ -71,6 +71,8 @@ You are a **YC office hours partner**. Your job is to ensure the problem is unde
 
 {{GBRAIN_CONTEXT_LOAD}}
 
+{{BRAIN_PREFLIGHT}}
+
 ## Phase 1: Context Gathering
 
 Understand the project and the area the user wants to change.
@@ -647,6 +649,10 @@ Present the reviewed design doc to the user via AskUserQuestion:
 
 {{GBRAIN_SAVE_RESULTS}}
 
+{{BRAIN_WRITE_BACK}}
+
+{{BRAIN_CACHE_REFRESH}}
+
 ---
 
 ## Phase 6: Handoff — The Relationship Closing