feat(#1355): detect-and-warn guard for claude-code agent-teams (#1371)

* feat(#1355): detect-and-warn guard for claude-code agent-teams

GSD's multi-agent orchestration can stall under claude-code's experimental
agent-teams (a subagent's completion fails to route to the orchestrator). Per
the maintainer decision, the accepted scope is a read-only detector + one
non-fatal warning — NOT the declined run_in_background/TaskOutput conversion.

- New Teams Status Module (src/teams-status.cts → gsd-core/bin/lib/teams-status.cjs):
  pure resolveTeamsStatus({runtime, env}) + thin CLI cmdTeamsStatus reusing
  resolveRuntime. active = strictly-truthy env flag AND runtime === 'claude'.
- Wire `gsd-tools query teams-status [--active]` (read-only; no capability
  registration needed — conformance gates govern features, not query commands).
- One non-fatal warning in plan-phase.md before the first Agent spawn, gated on
  `query teams-status --active`; zero behavior change on non-claude/teams-off.
- Hermeticity: clear CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS in run-tests.cjs +
  SESSION_ENV_KEYS. Docs reference + CONTEXT.md glossary. Built lib gitignored.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#1355): add changeset for teams-detect guard

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* test(#1355): bump plan-phase.md workflow size baseline (+407B for teams warning)

The non-fatal agent-teams warning block added to plan-phase.md grew it
92759 → 93166 bytes, past its committed per-file baseline ratchet. The growth
is small, deliberate, and still well under the workflow tier hard cap. Regenerate
the baseline via `npm run size:baseline` (only plan-phase.md changed).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(#1355): register teams-status.cjs in the inventory manifest

The new teams-status CLI module is a tracked surface; regenerate
docs/INVENTORY-MANIFEST.json (cli_modules family) via
gen-inventory-manifest.cjs --write so the inventory-manifest-sync gate passes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/teams-status.cts

@@ -0,0 +1,93 @@
+/**
+ * Teams Status Module — issue #1355
+ *
+ * Read-only detector for claude-code's experimental agent-teams feature.
+ * Exposes a PURE core function (env injected, no process.env/disk inside) and
+ * a thin CLI wrapper that reuses resolveRuntime from runtime-slash.cjs.
+ *
+ * Exports:
+ *   resolveTeamsStatus({ runtime, env }) → TeamsStatus
+ *   cmdTeamsStatus(cwd, opts)  — I/O entry point
+ *
+ * resolveTeamsStatus is PURE: env and runtime are injected, no process.env or
+ * disk access inside the function. Pass process.env explicitly at call sites.
+ *
+ * cmdTeamsStatus is the I/O handler. It reads process.env, resolves the
+ * runtime via resolveRuntime(cwd) from runtime-slash.cjs (GSD_RUNTIME →
+ * config.runtime → 'claude' precedence), then:
+ *   - default: prints JSON.stringify(status) to stdout via io.output, exits 0.
+ *   - --active: prints nothing, exits 0 if status.active, exit 1 otherwise.
+ *
+ * Strictly read-only — no config writes, no disk mutation.
+ *
+ * Dependencies:
+ *   - ./io.cjs             (output)
+ *   - ./runtime-slash.cjs  (resolveRuntime)
+ */
+
+// eslint-disable-next-line @typescript-eslint/no-require-imports
+import ioMod = require('./io.cjs');
+const { output: coreOutput } = ioMod;
+
+// ─── Types ────────────────────────────────────────────────────────────────────
+
+export interface TeamsStatus {
+  /** true only when env flag is strictly-truthy AND runtime === 'claude' */
+  active: boolean;
+  /** resolved runtime name */
+  runtime: string;
+  /** true when CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS is set to a truthy value */
+  env_present: boolean;
+  /** human-readable source description */
+  source: 'on: env' | 'off: flag absent' | 'off: non-claude';
+}
+
+// ─── Pure core ────────────────────────────────────────────────────────────────
+
+/**
+ * Resolve the agent-teams status from injected runtime and env.
+ *
+ * Strict truthiness: only '1' and 'true' (case-insensitive, trimmed) are on.
+ * '0', 'false', '', and unset are all off.
+ *
+ * @param opts.runtime  The resolved runtime name (e.g. 'claude', 'codex')
+ * @param opts.env      The environment map to read from (typically process.env)
+ */
+export function resolveTeamsStatus(opts: { runtime: string; env: NodeJS.ProcessEnv }): TeamsStatus {
+  const raw = (opts.env['CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS'] ?? '').trim().toLowerCase();
+  const envOn = raw === '1' || raw === 'true';          // strict: never '0'/'false'/'' as on
+  const isClaude = opts.runtime === 'claude';
+  const source = !isClaude ? 'off: non-claude' : (envOn ? 'on: env' : 'off: flag absent');
+  return { active: envOn && isClaude, runtime: opts.runtime, env_present: envOn, source };
+}
+
+// ─── CLI command handler ──────────────────────────────────────────────────────
+
+/**
+ * Command entry point: resolve runtime via resolveRuntime(cwd), read process.env,
+ * call resolveTeamsStatus, and emit the result.
+ *
+ * @param cwd       Project root directory (used by resolveRuntime for config.json)
+ * @param opts      Command options
+ * @param opts.active  When true: print nothing, exit 0 if active, exit 1 otherwise
+ */
+export function cmdTeamsStatus(cwd: string, opts: { active?: boolean }): void {
+  // Resolve runtime via the canonical precedence:
+  //   GSD_RUNTIME → config.runtime → 'claude'
+  // Reuses resolveRuntime from runtime-slash.cjs — no reimplementation.
+  // eslint-disable-next-line @typescript-eslint/no-require-imports
+  const runtimeSlash = require('./runtime-slash.cjs') as {
+    resolveRuntime: (projectDir: string | null | undefined) => string;
+  };
+  const runtime = runtimeSlash.resolveRuntime(cwd);
+
+  const status = resolveTeamsStatus({ runtime, env: process.env });
+
+  if (opts.active) {
+    // --active mode: no output, exit code encodes the boolean
+    process.exit(status.active ? 0 : 1);
+  }
+
+  // Default: emit JSON to stdout via io.output, exit 0
+  coreOutput(status, false);
+}