fix(gbrain): thin-client state — remote-MCP brains no longer classify as broken-config (#2051)

A thin client (remote-HTTP MCP brain, no local engine by design) probed
`gbrain sources list`, which gbrain's dispatch guard REFUSES on thin clients
(exit 1, no recognized error string), so the classifier fell to its
defensive broken-config default and every suppression gate silently hid
brain-aware blocks from exactly the users on a shared team brain.

New 'thin-client' state, detected PRE-probe from gbrain's own remote_mcp
config marker via the existing gbrainConfigPath() helper (mirrors gbrain's
isThinClient(); honors GBRAIN_HOME; zero network, immune to error-string
drift), with a /thin[- ]client/ stderr backstop in the probe catch. Remote
reachability is deliberately NOT probed by the classifier — that is the
#1964 pathology; gbrain calls degrade gracefully at use time, and the detect
JSON says so honestly (gbrain_thin_client: {probed: false}).

The state is admitted at every suppression gate — gstack-gbrain-detect
--is-ok (drives setup + gbrain-refresh), gen-skill-docs' detection override,
gstack-config gbrain-refresh — while the sync stages (code/memory/dream)
SKIP with an accurate reason: code indexing runs on the brain server, memory
syncs via the remote brain's artifacts pull. The two consumer classes need
opposite answers, which is why this is a distinct state and not a
skip-the-probe special case. sync-gbrain Step 1.5 and setup-gbrain prose
route thin-client to proceed, never into broken-config remediation.

detectMcpMode secondary generalization: url-match against the config's
remote_mcp.mcp_url (deterministic — gbrain mounts at the generic /mcp path)
-> name pattern gbrain[-_]* -> stdio command token; gbrain_mcp_mode stays a
3-value enum.

Tripwires: end-to-end --is-ok exits 0 on a thin-client fixture AND still
exits 1 on broken-config (the gate didn't widen); pre-probe + stderr-fallback
classifier paths; 4 detectMcpMode identification cases incl. a non-matching
url that must NOT false-positive.

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

sync-gbrain/SKILL.md.tmpl

@@ -139,6 +139,14 @@ BEFORE invoking the orchestrator:
   slow (cold pooler connection, #1964). Tell the user in one line: "Engine
   probe timed out (>15s) — proceeding; raise `GSTACK_GBRAIN_PROBE_TIMEOUT_MS`
   if your pooler is slow." Do NOT treat this as a broken config.
+- **`thin-client`**: proceed to Step 2 — this machine is a thin client of a
+  remote-HTTP MCP brain (#2051): no local engine BY DESIGN, so the code,
+  memory, and dream stages will SKIP with a thin-client reason (code indexing
+  runs on the brain server; memory syncs via the remote brain's artifacts
+  pull). Only the brain-sync push runs locally. Tell the user in one line:
+  "Thin client of a remote brain — local stages skip by design; brain queries
+  work via remote MCP (reachability is verified at use time, not probed
+  here)." Do NOT route this into the broken-config remediation.
 - **`no-cli`**: STOP. "Local gbrain CLI not installed. Run `/setup-gbrain`
   first."
 - **`missing-config`** AND `gbrain_mcp_mode == "remote-http"`: tell the user