feat(#2): consume GET /me + GET /capabilities via --whoami one-shot

v1 coverage-audit slice (capabilities+me). Both endpoints had no
caller; add them as cheap boot-time debug primitives.

- sessions.py: get_me (GET /me — identity/whoami) + get_capabilities
  (GET /capabilities — Echo ephemeral-template discovery). Mirror
  get_persona_state: 200 -> parsed dict verbatim, non-200 ->
  SessionApiFailed. Freeform dicts (frozen OpenAPI types both as
  objects).
- cli.py: new --whoami one-shot mode (mirrors --send). Fetches both,
  prints an identity + capabilities report, exits. Standalone probe:
  mutually exclusive with --send/--session/--new/--agent; opens no
  session. New ParsedArgs.whoami field + main() dispatch.
- Contract #2 amended (2 FNs) + validated. TDD: 5 wrapper tests +
  5 cli tests (validation + mode + error). Coverage map: REST 9/40.
  Suite 538 green; touched code ruff-clean.

Audit note: /capabilities is the Echo ephemeral-template discovery
endpoint, not a generic server-caps endpoint (coverage-map framing
corrected). TUI-surfacing of /me + /capabilities deferred.

tests/test_sessions.py

@@ -18,6 +18,8 @@ from ratatoskr.sessions import (
     SessionPage,
     create_session,
     endpoint_for_plane,
+    get_capabilities,
+    get_me,
     get_persona_state,
     list_agents,
     list_sessions,
@@ -896,3 +898,96 @@ class TestGetPersonaState:
             with pytest.raises(PersonaNotConfigured) as exc_info:
                 await get_persona_state(client, "domari")
         assert exc_info.value.agent_id == "domari"
+
+
+class TestGetMe:
+    """docs/contracts/issues/2.contract.md FN get_me (slice: capabilities+me)."""
+
+    @respx.mock
+    async def test_happy_authenticated(self) -> None:
+        """happy_authenticated [happy,tracer]: 200 → parsed identity dict verbatim."""
+        respx.get("https://w.example/me").mock(
+            return_value=httpx.Response(
+                200,
+                json={
+                    "user_id": "alice",
+                    "scopes": ["conversations.read", "conversations.write"],
+                    "tier": "user",
+                    "key_id": "a1b2c3d4",
+                    "key_label": "alice phone",
+                },
+            )
+        )
+        async with httpx.AsyncClient(base_url="https://w.example") as client:
+            me = await get_me(client)
+        assert me["user_id"] == "alice"
+        assert me["tier"] == "user"
+        assert me["key_id"] == "a1b2c3d4"
+        assert me["scopes"] == ["conversations.read", "conversations.write"]
+
+    @respx.mock
+    async def test_anonymous_dev_mode(self) -> None:
+        """anonymous_dev_mode: 200 anonymous shape → dict with tier=anonymous."""
+        respx.get("https://w.example/me").mock(
+            return_value=httpx.Response(
+                200,
+                json={
+                    "user_id": "anonymous",
+                    "scopes": ["conversations.read"],
+                    "tier": "anonymous",
+                },
+            )
+        )
+        async with httpx.AsyncClient(base_url="https://w.example") as client:
+            me = await get_me(client)
+        assert me["tier"] == "anonymous"
+        assert "key_id" not in me  # optional fields omitted, not null
+
+    @respx.mock
+    async def test_401_raises_session_api_failed(self) -> None:
+        """401_raises [error]: bad/absent key → SessionApiFailed(status=401)."""
+        respx.get("https://w.example/me").mock(
+            return_value=httpx.Response(401, json={"detail": "auth_invalid"})
+        )
+        async with httpx.AsyncClient(base_url="https://w.example") as client:
+            with pytest.raises(SessionApiFailed) as exc:
+                await get_me(client)
+        assert exc.value.status == 401
+
+
+class TestGetCapabilities:
+    """docs/contracts/issues/2.contract.md FN get_capabilities (slice: capabilities+me)."""
+
+    @respx.mock
+    async def test_happy(self) -> None:
+        """happy [happy]: 200 → ephemeral_templates dict verbatim."""
+        respx.get("https://w.example/capabilities").mock(
+            return_value=httpx.Response(
+                200,
+                json={
+                    "ephemeral_templates": {
+                        "echo": {
+                            "allowed_models": ["glm5-turbo", "glm4.7"],
+                            "default_model": "glm5-turbo",
+                            "system_prompt_max_bytes": 32768,
+                        }
+                    }
+                },
+            )
+        )
+        async with httpx.AsyncClient(base_url="https://w.example") as client:
+            caps = await get_capabilities(client)
+        echo = caps["ephemeral_templates"]["echo"]
+        assert echo["default_model"] == "glm5-turbo"
+        assert echo["system_prompt_max_bytes"] == 32768
+
+    @respx.mock
+    async def test_non_200_raises(self) -> None:
+        """non_200_raises [error]: 500 → SessionApiFailed(status=500)."""
+        respx.get("https://w.example/capabilities").mock(
+            return_value=httpx.Response(500, content=b"boom")
+        )
+        async with httpx.AsyncClient(base_url="https://w.example") as client:
+            with pytest.raises(SessionApiFailed) as exc:
+                await get_capabilities(client)
+        assert exc.value.status == 500