feat(#2): consume GET /sessions/{id}/tools — Tools-pane inventory hydrate

v1 coverage-audit Tier-2 quick win. The owner-scoped tool-inventory
endpoint (#183) had no caller; wire it into the TUI Tools pane.

- sessions.py: get_session_tools (GET /sessions/{id}/tools) — owner-
  scoped (consumer key, no admin scope), 200 -> parsed dict verbatim,
  non-200 -> SessionApiFailed. Mirrors get_persona_state / get_me.
- tui.py: _format_tool_inventory helper + _hydrate_session_tools
  best-effort worker (mirrors _hydrate_persona), wired unconditionally
  in on_mount. Writes the merged {agent_id, builtin_tools,
  bifrost_tools} inventory the LLM saw at turn-fire into the Tools
  pane + audits; never crashes on failure.
- Covers the design-brief 5 "Tools widget" via the reachable owner
  endpoint (the admin variant stays a gap only for cross-user debug).
- Contract #2 amended (FN) + validated. TDD: 3 wrapper tests + 1
  format-helper unit + 2 hydrate integration tests. Coverage: REST
  10/40. Suite 544 green; touched code ruff-clean.

tests/test_tui.py

@@ -3167,3 +3167,71 @@ class TestBareSessionPicker:
         assert rc == 20
         assert "[session_api_failed]" in capsys.readouterr().err
         assert not opened
+
+
+class TestSessionToolsHydration:
+    """get_session_tools + the #183 Tools-pane inventory hydrate (GET /sessions/{id}/tools)."""
+
+    def test_format_tool_inventory(self) -> None:
+        """format_tool_inventory [unit]: header + builtin + bifrost lines."""
+        from ratatoskr.tui import _format_tool_inventory
+
+        lines = _format_tool_inventory(
+            {
+                "agent_id": "alice:wizard",
+                "builtin_tools": [],
+                "bifrost_tools": [{"name": "bifrost.x"}, {"name": "bifrost.y"}],
+            }
+        )
+        joined = "\n".join(lines)
+        assert "agent=alice:wizard" in joined
+        assert "builtin=0 bifrost=2" in joined
+        assert "builtin: (none)" in joined
+        assert "bifrost.x, bifrost.y" in joined
+
+    async def test_hydrate_writes_inventory_and_audits(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """hydrate_writes_inventory [scenario,tracer]: 200 → inventory in Tools pane + audit."""
+        import ratatoskr.tui as tui_mod
+
+        writes = _spy_writes(monkeypatch)
+
+        async def fake_tools(client, session_id):
+            return {
+                "agent_id": "alice:wizard",
+                "builtin_tools": [],
+                "bifrost_tools": [{"name": "bifrost.set_field"}],
+            }
+
+        monkeypatch.setattr(tui_mod, "get_session_tools", fake_tools)
+        app = _resolved_app(_args_existing(session_id="s-tools-01"))
+        async with app.run_test() as pilot:
+            await pilot.pause()
+            await app._hydrate_session_tools()
+            await pilot.pause()
+        joined = " ".join(_text_of(w) for w in writes)
+        assert "session tool inventory" in joined
+        assert "bifrost.set_field" in joined
+        assert "session_tools_hydrated" in joined  # audit line landed
+
+    async def test_hydrate_failure_audits_no_crash(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """hydrate_failure [error]: get_session_tools raises → failure audit; no crash."""
+        import ratatoskr.tui as tui_mod
+        from ratatoskr.sessions import SessionApiFailed
+
+        writes = _spy_writes(monkeypatch)
+
+        async def boom(client, session_id):
+            raise SessionApiFailed(status=404, body=b"session_not_found")
+
+        monkeypatch.setattr(tui_mod, "get_session_tools", boom)
+        app = _resolved_app(_args_existing(session_id="s-tools-02"))
+        async with app.run_test() as pilot:
+            await pilot.pause()
+            await app._hydrate_session_tools()
+            await pilot.pause()
+        joined = " ".join(_text_of(w) for w in writes)
+        assert "session_tools_hydration_failed" in joined