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>

docs/CLI-TOOLS.md

@@ -206,6 +206,48 @@ node gsd-tools.cjs capability set code-review --gate workflow.code_review=false
 
 ---
 
+## Teams Status
+
+### `query teams-status`
+
+```bash
+node gsd-tools.cjs query teams-status [--active]
+```
+
+Read-only detector for claude-code's experimental agent-teams feature (issue #1355). Resolves the runtime via the canonical `GSD_RUNTIME` → `config.runtime` → `'claude'` precedence, then checks `CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS`.
+
+**Default (no flags):** prints a JSON object and exits 0:
+
+```json
+{
+  "active": false,
+  "runtime": "claude",
+  "env_present": false,
+  "source": "off: flag absent"
+}
+```
+
+Fields:
+
+| Field | Type | Description |
+|---|---|---|
+| `active` | boolean | `true` only when `CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS` is strictly truthy (`"1"` or `"true"`, case-insensitive) **and** the resolved runtime is `"claude"` |
+| `runtime` | string | The resolved runtime name (e.g. `"claude"`, `"codex"`) |
+| `env_present` | boolean | `true` when the env flag is set to a strictly-truthy value |
+| `source` | string | One of: `"on: env"`, `"off: flag absent"`, `"off: non-claude"` |
+
+**`--active` flag:** exits 0 if `active` is true, exits 1 otherwise. Prints nothing. Useful in bash conditionals:
+
+```bash
+if gsd_run query teams-status --active >/dev/null 2>&1; then
+  echo "agent-teams is on"
+fi
+```
+
+This command is strictly read-only — no config writes, no disk mutation.
+
+---
+
 ## Model Resolution
 
 ```bash

docs/INVENTORY-MANIFEST.json

@@ -371,6 +371,7 @@
       "state.cjs",
       "surface.cjs",
       "task-command-router.cjs",
+      "teams-status.cjs",
       "template.cjs",
       "uat-predicate.cjs",
       "uat.cjs",