v1.26.3.0 feat: /sync-gbrain skill + native code-surface orchestrator (#1314)

* feat: native gbrain code-surface orchestrator + ensureSourceRegistered helper

Replaces gbrain import (markdown only) with gbrain sources add + sync
--strategy code (or reindex-code on --full). Adds lib/gbrain-sources.ts
exporting ensureSourceRegistered/probeSource/sourcePageCount, plus lock
file + tmp-rename atomicity + dry-run write skip in the orchestrator.

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

* feat: setup-gbrain Step 8 writes ## GBrain Search Guidance after smoke test

Extends Step 8 to write a machine-agnostic guidance block that teaches
the agent when to prefer gbrain CLI (search/query/code-def/code-refs/
code-callers/code-callees) over Grep. Gated on smoke test pass.

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

* feat: /sync-gbrain skill — keep gbrain current and refresh agent guidance

New top-level skill that wraps gstack-gbrain-sync with state probing,
capability check (write+search round-trip, not gbrain doctor), CLAUDE.md
guidance lifecycle (write iff healthy, remove iff broken), and a
per-source verdict block. Re-runnable, idempotent.

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

* feat: preamble emits gbrain-availability block when capability ok

Extends generate-brain-sync-block.ts to emit Variant A (steady-state, 4
lines) when cwd page_count > 0 or Variant B (empty-corpus emergency, 3
lines) when 0; empty string otherwise. Reads cached page_count from
.gbrain-sync-state.json (handles pretty + compact JSON). Refreshes ship
golden fixtures and bumps the plan-review preamble byte budget to 35K
to absorb the new block.

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

* docs: register /sync-gbrain in AGENTS.md and docs/skills.md

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

* chore: regenerate SKILL.md across all hosts (gen:skill-docs)

Mechanical regeneration after preamble + setup-gbrain template + new
sync-gbrain skill. Run via: bun run gen:skill-docs --host all.

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

* chore: bump version and changelog (v1.26.3.0)

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

* docs: add /sync-gbrain to README skills table and gbrain section

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

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

docs/skills.md

@@ -42,6 +42,7 @@ Detailed guides for every gstack skill — philosophy, workflow, and examples.
 | [`/codex`](#codex) | **Second Opinion** | Independent review from OpenAI Codex CLI. Three modes: code review (pass/fail gate), adversarial challenge, and open consultation with session continuity. Cross-model analysis when both `/review` and `/codex` have run. |
 | [`/pair-agent`](#pair-agent) | **Remote Agent Bridge** | Pair a remote AI agent (OpenClaw, Codex, Cursor, Hermes) with your browser. Scoped tunnel, locked allowlist, session token. |
 | [`/setup-gbrain`](#setup-gbrain) | **Memory Sync** | Set up gbrain for cross-machine session memory sync. One command from zero to live. |
+| [`/sync-gbrain`](#sync-gbrain) | **Keep Brain Current** | Refresh gbrain against this repo's code; teach the agent when to use `gbrain search`/`code-def` over Grep. Idempotent; safe to re-run. |
 | | | |
 | **Safety & Utility** | | |
 | [`/careful`](#safety--guardrails) | **Safety Guardrails** | Warns before destructive commands (rm -rf, DROP TABLE, force-push, git reset --hard). Override any warning. Common build cleanups whitelisted. |