fix: read project-scoped MCP registrations in gbrain detection (#2499)

Claude Code registers MCP servers at two scopes in ~/.claude.json: user
scope (.mcpServers) and project scope (.projects["/abs/path"].mcpServers
— what `claude mcp add` WITHOUT --scope user writes). Every gbrain
detection site read only user scope, so a correctly configured
project-scoped brain was invisible: brain-aware blocks suppressed,
remote-mode artifacts sync never recognised, and detectEndpointHash fell
through to the 'local' literal — two different project-scoped brains
hashed identically, so switching between them never invalidated the
cache, the exact scenario the function's docstring says it exists to
catch. Nothing errored; the features just quietly were not there.

Two sites fixed:

- scripts/resolvers/preamble/generate-brain-sync-block.ts: the shared
  detection block (rendered into every tier-2+ SKILL.md) now resolves the
  gbrain entry ONCE into _GBRAIN_MCP_ENTRY — user scope first, then the
  nearest-ancestor project entry for $PWD that actually carries a gbrain
  server (longest matching key with a path-boundary check: /a/repo never
  matches /a/repo2; a nested project WITHOUT gbrain doesn't shadow its
  parent's registration). _GBRAIN_MCP_TYPE and _GBRAIN_HOST extract from
  the resolved entry, so claude.json is parsed once per skill start. All
  SKILL.md files regenerated in this commit; the ship golden fixtures and
  three carve-guard skeleton caps (plan-eng-review, plan-devex-review,
  office-hours; ~1.5KB rendered growth per skill) are refreshed with
  measured values.
- bin/gstack-brain-cache detectEndpointHash: same resolution order in TS
  (user scope, else nearest-ancestor project entry by cwd, both path
  separators for Windows keys).

Tests: rendered-output tests in test/gen-skill-docs.test.ts pin the
regenerated block (static markers + a FUNCTIONAL run of the exact
rendered lines against a fixture ~/.claude.json with only a
project-scoped registration, plus an outside-cwd discriminator);
detectEndpointHash unit tests in test/brain-cache-roundtrip.test.ts cover
project-scope resolve, path-boundary, nearest-ancestor distinct hashes,
and user-scope precedence.

Root-cause analysis by @samporter-31 in #2499.

Fixes #2499

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

codex/SKILL.md

@@ -507,10 +507,13 @@ _BRAIN_SYNC_MODE=$("$_BRAIN_CONFIG_BIN" get artifacts_sync_mode 2>/dev/null || e
 # Detect remote-MCP mode (Path 4 of /setup-gbrain). Local artifacts sync is
 # a no-op in remote mode; the brain server pulls from GitHub/GitLab on its
 # own cadence. Read claude.json directly to keep this preamble fast (no
-# subprocess to claude CLI on every skill start).
+# subprocess to claude CLI on every skill start). Both registration scopes
+# are read (#2499): user scope, then the nearest-ancestor project scope.
 _GBRAIN_MCP_MODE="none"
+_GBRAIN_MCP_ENTRY=""
 if command -v jq >/dev/null 2>&1 && [ -f "$HOME/.claude.json" ]; then
-  _GBRAIN_MCP_TYPE=$(jq -r '.mcpServers.gbrain.type // .mcpServers.gbrain.transport // empty' "$HOME/.claude.json" 2>/dev/null)
+  _GBRAIN_MCP_ENTRY=$(jq -c --arg cwd "$PWD" '.mcpServers.gbrain // ((.projects // {}) | to_entries | map(select((.key as $k | $cwd == $k or ($cwd | startswith($k + "/"))) and ((try .value.mcpServers.gbrain catch null) != null))) | sort_by(.key | length) | last | .value.mcpServers.gbrain) // empty' "$HOME/.claude.json" 2>/dev/null)
+  _GBRAIN_MCP_TYPE=$(printf '%s' "$_GBRAIN_MCP_ENTRY" | jq -r '.type // .transport // empty' 2>/dev/null)
   case "$_GBRAIN_MCP_TYPE" in
     url|http|sse) _GBRAIN_MCP_MODE="remote-http" ;;
     stdio) _GBRAIN_MCP_MODE="local-stdio" ;;
@@ -545,7 +548,7 @@ fi
 if [ "$_GBRAIN_MCP_MODE" = "remote-http" ]; then
   # Remote-MCP mode: local artifacts sync is a no-op (brain admin's server
   # pulls from GitHub/GitLab). Show the user this is by design, not broken.
-  _GBRAIN_HOST=$(jq -r '.mcpServers.gbrain.url // empty' "$HOME/.claude.json" 2>/dev/null | sed -E 's|^https?://([^/:]+).*|\1|' | head -1 | tr -cd 'A-Za-z0-9._-')
+  _GBRAIN_HOST=$(printf '%s' "${_GBRAIN_MCP_ENTRY:-}" | jq -r '.url // empty' 2>/dev/null | sed -E 's|^https?://([^/:]+).*|\1|' | head -1 | tr -cd 'A-Za-z0-9._-')
   echo "ARTIFACTS_SYNC: remote-mode (managed by brain server ${_GBRAIN_HOST:-remote})"
 elif [ -d "$_GSTACK_HOME/.git" ] && [ "$_BRAIN_SYNC_MODE" != "off" ]; then
   _BRAIN_QUEUE_DEPTH=0