diff --git a/bin/gstack-gbrain-detect b/bin/gstack-gbrain-detect
index 526ff82d..d672cde0 100755
--- a/bin/gstack-gbrain-detect
+++ b/bin/gstack-gbrain-detect
@@ -11,8 +11,10 @@
 #     "gbrain_config_exists": true|false,
 #     "gbrain_engine": "pglite"|"postgres" | null,
 #     "gbrain_doctor_ok": true|false,
+#     "gbrain_mcp_mode": "local-stdio"|"remote-http"|"none",
 #     "gstack_brain_sync_mode": "off"|"artifacts-only"|"full",
-#     "gstack_brain_git": true|false
+#     "gstack_brain_git": true|false,
+#     "gstack_artifacts_remote": "https://..." | ""
 #   }
 #
 # The /setup-gbrain skill reads this once at startup to decide which path
@@ -92,6 +94,76 @@ if [ -d "$STATE_DIR/.git" ]; then
   gstack_brain_git=true
 fi
 
+# --- gbrain_mcp_mode: local-stdio | remote-http | none ---
+# Defense-in-depth fallback chain (intentional ordering, do not reorder):
+#   1. `claude mcp get gbrain --json` — public CLI surface, structured output
+#   2. `claude mcp list` text-grep    — older claude versions without --json
+#   3. `~/.claude.json` jq read       — last resort if `claude` isn't on PATH
+# Fallback chain logged because if Anthropic moves the file or renames keys,
+# the third tier breaks silently; the first two tiers should catch it.
+gbrain_mcp_mode="none"
+if command -v claude >/dev/null 2>&1; then
+  # Tier 1: claude mcp get --json
+  if mcp_get_json=$(claude mcp get gbrain --json 2>/dev/null); then
+    if echo "$mcp_get_json" | jq -e '.' >/dev/null 2>&1; then
+      mtype=$(echo "$mcp_get_json" | jq -r '.type // .transport // empty' 2>/dev/null)
+      mcommand=$(echo "$mcp_get_json" | jq -r '.command // empty' 2>/dev/null)
+      murl=$(echo "$mcp_get_json" | jq -r '.url // empty' 2>/dev/null)
+      case "$mtype" in
+        http|sse) gbrain_mcp_mode="remote-http" ;;
+        stdio)    gbrain_mcp_mode="local-stdio" ;;
+        *)
+          # Newer claude versions may emit just url + command; infer.
+          if [ -n "$murl" ]; then gbrain_mcp_mode="remote-http"
+          elif [ -n "$mcommand" ]; then gbrain_mcp_mode="local-stdio"
+          fi
+          ;;
+      esac
+    fi
+  fi
+  # Tier 2: claude mcp list text-grep (only if Tier 1 didn't resolve)
+  if [ "$gbrain_mcp_mode" = "none" ]; then
+    if mcp_list=$(claude mcp list 2>/dev/null); then
+      gbrain_line=$(echo "$mcp_list" | grep -E '^gbrain:' || true)
+      if [ -n "$gbrain_line" ]; then
+        if echo "$gbrain_line" | grep -q 'http\|HTTP'; then
+          gbrain_mcp_mode="remote-http"
+        else
+          gbrain_mcp_mode="local-stdio"
+        fi
+      fi
+    fi
+  fi
+fi
+# Tier 3: ~/.claude.json jq read (only if claude binary or earlier tiers failed)
+if [ "$gbrain_mcp_mode" = "none" ]; then
+  if [ -f "$HOME/.claude.json" ]; then
+    # Look for a gbrain MCP server entry. Type field disambiguates http vs stdio.
+    mtype=$(jq -r '.mcpServers.gbrain.type // .mcpServers.gbrain.transport // empty' "$HOME/.claude.json" 2>/dev/null)
+    murl=$(jq -r '.mcpServers.gbrain.url // empty' "$HOME/.claude.json" 2>/dev/null)
+    mcommand=$(jq -r '.mcpServers.gbrain.command // empty' "$HOME/.claude.json" 2>/dev/null)
+    case "$mtype" in
+      url|http|sse) gbrain_mcp_mode="remote-http" ;;
+      stdio)        gbrain_mcp_mode="local-stdio" ;;
+      *)
+        if [ -n "$murl" ]; then gbrain_mcp_mode="remote-http"
+        elif [ -n "$mcommand" ]; then gbrain_mcp_mode="local-stdio"
+        fi
+        ;;
+    esac
+  fi
+fi
+
+# --- artifacts remote URL (post-rename) with brain-* fallback during the
+#     migration window (gstack-upgrade migration runs the rename). ---
+gstack_artifacts_remote=""
+if [ -f "$HOME/.gstack-artifacts-remote.txt" ]; then
+  gstack_artifacts_remote=$(head -1 "$HOME/.gstack-artifacts-remote.txt" 2>/dev/null | tr -d '[:space:]' || true)
+elif [ -f "$HOME/.gstack-brain-remote.txt" ]; then
+  # Pre-migration fallback. Migration v1.27.0.0 will mv this to the new path.
+  gstack_artifacts_remote=$(head -1 "$HOME/.gstack-brain-remote.txt" 2>/dev/null | tr -d '[:space:]' || true)
+fi
+
 # Emit single-object JSON.
 jq -n \
   --argjson on_path "$gbrain_on_path" \
@@ -99,14 +171,18 @@ jq -n \
   --argjson config_exists "$gbrain_config_exists" \
   --argjson engine "$gbrain_engine" \
   --argjson doctor_ok "$gbrain_doctor_ok" \
+  --arg mcp_mode "$gbrain_mcp_mode" \
   --arg sync_mode "$gstack_brain_sync_mode" \
   --argjson brain_git "$gstack_brain_git" \
+  --arg artifacts_remote "$gstack_artifacts_remote" \
   '{
     gbrain_on_path: $on_path,
     gbrain_version: $version,
     gbrain_config_exists: $config_exists,
     gbrain_engine: $engine,
     gbrain_doctor_ok: $doctor_ok,
+    gbrain_mcp_mode: $mcp_mode,
     gstack_brain_sync_mode: $sync_mode,
-    gstack_brain_git: $brain_git
+    gstack_brain_git: $brain_git,
+    gstack_artifacts_remote: $artifacts_remote
   }'
diff --git a/test/gstack-gbrain-detect-mcp-mode.test.ts b/test/gstack-gbrain-detect-mcp-mode.test.ts
new file mode 100644
index 00000000..052583d3
--- /dev/null
+++ b/test/gstack-gbrain-detect-mcp-mode.test.ts
@@ -0,0 +1,275 @@
+/**
+ * gstack-gbrain-detect — gbrain_mcp_mode + gstack_artifacts_remote tests.
+ *
+ * The script has a 3-tier fallback chain for resolving gbrain_mcp_mode:
+ *   1. `claude mcp get gbrain --json` (preferred — public CLI surface)
+ *   2. `claude mcp list` text-grep (older claude versions without --json)
+ *   3. `~/.claude.json` jq read (fallback if claude binary is absent)
+ *
+ * Each layer is tested by mocking the layer it depends on. Per codex
+ * Finding #3 (defense-in-depth ordering): if Anthropic moves the
+ * ~/.claude.json file format, the first two tiers should still work.
+ */
+
+import { describe, test, expect, beforeEach, afterEach } from 'bun:test';
+import * as fs from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import { spawnSync } from 'child_process';
+
+const ROOT = path.resolve(import.meta.dir, '..');
+const DETECT_BIN = path.join(ROOT, 'bin', 'gstack-gbrain-detect');
+
+let tmpHome: string;
+let fakeBinDir: string;
+
+function makeFakeClaude(opts: {
+  hasGetJson?: boolean;
+  getJsonOutput?: string; // raw JSON string
+  hasMcpList?: boolean;
+  mcpListOutput?: string;
+  exitOnAll?: number; // if set, claude always exits with this code
+}) {
+  const { hasGetJson, getJsonOutput, hasMcpList, mcpListOutput, exitOnAll } = opts;
+  const script = `#!/bin/bash
+${exitOnAll !== undefined ? `exit ${exitOnAll}` : ''}
+case "$1 $2" in
+  "mcp get")
+    if [ "$3" = "gbrain" ] && [ "$4" = "--json" ]; then
+      ${hasGetJson ? `cat <<'JSON'
+${getJsonOutput || '{}'}
+JSON` : 'exit 1'}
+      exit 0
+    fi
+    ;;
+  "mcp list")
+    ${hasMcpList ? `cat <<'EOM'
+${mcpListOutput || ''}
+EOM` : 'exit 1'}
+    exit 0
+    ;;
+esac
+exit 1
+`;
+  fs.writeFileSync(path.join(fakeBinDir, 'claude'), script, { mode: 0o755 });
+}
+
+function runDetect(extraEnv: Record<string, string> = {}): { code: number; json: any; stderr: string } {
+  const realPath = process.env.PATH ?? '';
+  const r = spawnSync(DETECT_BIN, [], {
+    env: {
+      // Put fakeBinDir first so our claude shim wins; include the project bin
+      // for any sibling scripts and standard paths for jq/etc.
+      PATH: `${fakeBinDir}:${path.join(ROOT, 'bin')}:${realPath}`,
+      HOME: tmpHome,
+      GSTACK_HOME: path.join(tmpHome, '.gstack'),
+      ...extraEnv,
+    },
+    encoding: 'utf-8',
+  });
+  let json: any = null;
+  try {
+    json = JSON.parse(r.stdout || '{}');
+  } catch {
+    json = null;
+  }
+  return { code: r.status ?? -1, json, stderr: r.stderr || '' };
+}
+
+beforeEach(() => {
+  tmpHome = fs.mkdtempSync(path.join(os.tmpdir(), 'detect-mcp-mode-'));
+  fakeBinDir = fs.mkdtempSync(path.join(os.tmpdir(), 'detect-fake-bin-'));
+});
+
+afterEach(() => {
+  fs.rmSync(tmpHome, { recursive: true, force: true });
+  fs.rmSync(fakeBinDir, { recursive: true, force: true });
+});
+
+describe('gbrain_mcp_mode — Tier 1: claude mcp get --json', () => {
+  test('type=http → remote-http', () => {
+    makeFakeClaude({
+      hasGetJson: true,
+      getJsonOutput: JSON.stringify({ type: 'http', url: 'https://example.com/mcp' }),
+    });
+    const r = runDetect();
+    expect(r.code).toBe(0);
+    expect(r.json.gbrain_mcp_mode).toBe('remote-http');
+  });
+
+  test('type=stdio → local-stdio', () => {
+    makeFakeClaude({
+      hasGetJson: true,
+      getJsonOutput: JSON.stringify({ type: 'stdio', command: '/usr/local/bin/gbrain' }),
+    });
+    expect(runDetect().json.gbrain_mcp_mode).toBe('local-stdio');
+  });
+
+  test('type=sse → remote-http', () => {
+    makeFakeClaude({
+      hasGetJson: true,
+      getJsonOutput: JSON.stringify({ type: 'sse', url: 'https://example.com/sse' }),
+    });
+    expect(runDetect().json.gbrain_mcp_mode).toBe('remote-http');
+  });
+
+  test('no type field but has url → remote-http (newer claude shape)', () => {
+    makeFakeClaude({
+      hasGetJson: true,
+      getJsonOutput: JSON.stringify({ url: 'https://example.com/mcp' }),
+    });
+    expect(runDetect().json.gbrain_mcp_mode).toBe('remote-http');
+  });
+
+  test('no type field but has command → local-stdio', () => {
+    makeFakeClaude({
+      hasGetJson: true,
+      getJsonOutput: JSON.stringify({ command: '/path/to/gbrain' }),
+    });
+    expect(runDetect().json.gbrain_mcp_mode).toBe('local-stdio');
+  });
+});
+
+describe('gbrain_mcp_mode — Tier 2: claude mcp list text-grep', () => {
+  test('falls back to mcp list when get --json fails', () => {
+    makeFakeClaude({
+      hasGetJson: false,
+      hasMcpList: true,
+      mcpListOutput: 'gbrain: https://wintermute.tail554574.ts.net:3131/mcp (HTTP) - ✓ Connected',
+    });
+    expect(runDetect().json.gbrain_mcp_mode).toBe('remote-http');
+  });
+
+  test('mcp list text-grep with stdio entry → local-stdio', () => {
+    makeFakeClaude({
+      hasGetJson: false,
+      hasMcpList: true,
+      mcpListOutput: 'gbrain: /usr/local/bin/gbrain serve - ✓ Connected',
+    });
+    expect(runDetect().json.gbrain_mcp_mode).toBe('local-stdio');
+  });
+
+  test('mcp list with no gbrain entry → none', () => {
+    makeFakeClaude({
+      hasGetJson: false,
+      hasMcpList: true,
+      mcpListOutput: 'posthog: https://mcp.posthog.com/mcp (HTTP)\nslack: https://slack.com/mcp (HTTP)',
+    });
+    expect(runDetect().json.gbrain_mcp_mode).toBe('none');
+  });
+});
+
+describe('gbrain_mcp_mode — Tier 3: ~/.claude.json jq read', () => {
+  test('reads mcpServers.gbrain.type=url → remote-http', () => {
+    // No fake claude binary; force fallback to file read.
+    fs.writeFileSync(
+      path.join(tmpHome, '.claude.json'),
+      JSON.stringify({
+        mcpServers: { gbrain: { type: 'url', url: 'https://example.com/mcp' } },
+      })
+    );
+    expect(runDetect().json.gbrain_mcp_mode).toBe('remote-http');
+  });
+
+  test('reads mcpServers.gbrain.type=stdio → local-stdio', () => {
+    fs.writeFileSync(
+      path.join(tmpHome, '.claude.json'),
+      JSON.stringify({
+        mcpServers: { gbrain: { type: 'stdio', command: '/path/gbrain' } },
+      })
+    );
+    expect(runDetect().json.gbrain_mcp_mode).toBe('local-stdio');
+  });
+
+  test('infers from url field if type is missing', () => {
+    fs.writeFileSync(
+      path.join(tmpHome, '.claude.json'),
+      JSON.stringify({
+        mcpServers: { gbrain: { url: 'https://example.com/mcp' } },
+      })
+    );
+    expect(runDetect().json.gbrain_mcp_mode).toBe('remote-http');
+  });
+
+  test('infers from command field if type is missing', () => {
+    fs.writeFileSync(
+      path.join(tmpHome, '.claude.json'),
+      JSON.stringify({
+        mcpServers: { gbrain: { command: '/path/gbrain' } },
+      })
+    );
+    expect(runDetect().json.gbrain_mcp_mode).toBe('local-stdio');
+  });
+
+  test('no gbrain entry in ~/.claude.json → none', () => {
+    fs.writeFileSync(
+      path.join(tmpHome, '.claude.json'),
+      JSON.stringify({ mcpServers: { posthog: { type: 'url', url: 'https://x' } } })
+    );
+    expect(runDetect().json.gbrain_mcp_mode).toBe('none');
+  });
+});
+
+describe('gbrain_mcp_mode — no info anywhere', () => {
+  test('no claude binary AND no ~/.claude.json → none', () => {
+    // No fake claude, no file.
+    expect(runDetect().json.gbrain_mcp_mode).toBe('none');
+  });
+});
+
+describe('gstack_artifacts_remote', () => {
+  test('reads ~/.gstack-artifacts-remote.txt when present', () => {
+    fs.writeFileSync(
+      path.join(tmpHome, '.gstack-artifacts-remote.txt'),
+      'https://github.com/garrytan/gstack-artifacts-garrytan\n'
+    );
+    expect(runDetect().json.gstack_artifacts_remote).toBe(
+      'https://github.com/garrytan/gstack-artifacts-garrytan'
+    );
+  });
+
+  test('migration-window fallback: reads ~/.gstack-brain-remote.txt if artifacts file is missing', () => {
+    fs.writeFileSync(
+      path.join(tmpHome, '.gstack-brain-remote.txt'),
+      'git@github.com:garrytan/gstack-brain-garrytan.git\n'
+    );
+    expect(runDetect().json.gstack_artifacts_remote).toBe(
+      'git@github.com:garrytan/gstack-brain-garrytan.git'
+    );
+  });
+
+  test('artifacts file wins over brain file when both exist', () => {
+    fs.writeFileSync(
+      path.join(tmpHome, '.gstack-artifacts-remote.txt'),
+      'https://github.com/x/new\n'
+    );
+    fs.writeFileSync(
+      path.join(tmpHome, '.gstack-brain-remote.txt'),
+      'https://github.com/x/old\n'
+    );
+    expect(runDetect().json.gstack_artifacts_remote).toBe('https://github.com/x/new');
+  });
+
+  test('empty when neither file exists', () => {
+    expect(runDetect().json.gstack_artifacts_remote).toBe('');
+  });
+});
+
+describe('schema regression', () => {
+  test('output JSON has all expected keys (sync-gbrain compat)', () => {
+    const r = runDetect();
+    expect(r.code).toBe(0);
+    const keys = Object.keys(r.json).sort();
+    expect(keys).toEqual([
+      'gbrain_config_exists',
+      'gbrain_doctor_ok',
+      'gbrain_engine',
+      'gbrain_mcp_mode',
+      'gbrain_on_path',
+      'gbrain_version',
+      'gstack_artifacts_remote',
+      'gstack_brain_git',
+      'gstack_brain_sync_mode',
+    ]);
+  });
+});