fix(transcript): degrade session_transcript when no kb resolves

src/vouch/jsonl_server.py

@@ -84,6 +84,19 @@ def _store() -> KBStore:
         raise RuntimeError(str(e)) from e
 
 
+def _store_or_none() -> KBStore | None:
+    """The KB when one resolves, else None.
+
+    Only for reads whose data source is outside `.vouch/` — the KB is an
+    enrichment, not the subject. Every method that reads or writes knowledge
+    must keep using `_store()` so a missing KB stays a hard error.
+    """
+    try:
+        return _store()
+    except RuntimeError:
+        return None
+
+
 def _agent() -> str:
     # An authenticated bearer subject is the principal's real identity; it must
     # win over the client-supplied X-Vouch-Agent header (and VOUCH_AGENT env),
@@ -477,7 +490,7 @@ def _h_session_transcript(p: dict) -> dict:
     agent = p.get("agent")
     if agent is not None and agent not in ("claude", "codex"):
         raise ValueError(f"unknown agent: {agent!r} (expected 'claude' or 'codex')")
-    return transcript.load_transcript(_store(), session_id, agent=agent)
+    return transcript.load_transcript(_store_or_none(), session_id, agent=agent)
 
 
 def _h_propose_entity(p: dict) -> dict:

src/vouch/server.py

@@ -70,6 +70,19 @@ def _store() -> KBStore:
         ) from e
 
 
+def _store_or_none() -> KBStore | None:
+    """The KB when one resolves, else None.
+
+    Only for reads whose data source is outside `.vouch/` — the KB is an
+    enrichment, not the subject. Every method that reads or writes knowledge
+    must keep using `_store()` so a missing KB stays a hard error.
+    """
+    try:
+        return _store()
+    except RuntimeError:
+        return None
+
+
 def _agent() -> str:
     # An authenticated bearer subject (set by the /mcp transport) is the
     # principal's real identity and must be what proposals/audit attribute to,
@@ -685,12 +698,13 @@ def kb_session_transcript(session_id: str, agent: str | None = None) -> dict[str
     Read-only. Locates the raw Claude Code / Codex file on disk and normalizes
     it into message blocks (text, thinking, tool_use with paired results).
     ``agent`` restricts the search ("claude" | "codex"); omit to try both.
-    Degrades to compact capture observations when the raw file is unavailable.
+    Degrades to compact capture observations when the raw file is unavailable,
+    and to a bare unavailable result when no KB resolves at all.
     """
     from . import transcript
     if agent is not None and agent not in ("claude", "codex"):
         raise ValueError(f"unknown agent: {agent!r} (expected 'claude' or 'codex')")
-    return transcript.load_transcript(_store(), session_id, agent=agent)
+    return transcript.load_transcript(_store_or_none(), session_id, agent=agent)
 
 
 @mcp.tool()

src/vouch/transcript.py

@@ -374,19 +374,26 @@ def flush() -> None:
     return {"session": session, "messages": messages, "truncated": truncated}
 
 
-def _degraded(store: KBStore, session_id: str, reason: str) -> dict[str, Any]:
-    obs = _read_observations(buffer_path(store, session_id))
+def _degraded(store: KBStore | None, session_id: str, reason: str) -> dict[str, Any]:
+    # No KB resolved: the raw transcript lives outside `.vouch/`, so the
+    # lookup still answers — there is just no capture buffer to fall back on.
+    obs = _read_observations(buffer_path(store, session_id)) if store is not None else []
     return {"available": False, "reason": reason, "observations": obs}
 
 
 def load_transcript(
-    store: KBStore, session_id: str, *, agent: str | None = None
+    store: KBStore | None, session_id: str, *, agent: str | None = None
 ) -> dict[str, Any]:
     """Locate + parse the raw transcript for ``session_id``.
 
     ``agent`` restricts the search ("claude" | "codex"); when None both are
     tried. Returns the normalized schema on success, or a degraded result
     (compact capture observations) when the raw file is missing/too large.
+
+    ``store`` may be None when no KB resolves from the caller's cwd. The raw
+    transcript is read from the agent's own directory, not from the KB, so the
+    normalized result is unaffected; only the degraded path loses its
+    observations.
     """
     path: Path | None = None
     source_agent = ""

tests/test_session_transcript.py

@@ -215,6 +215,52 @@ def test_handler_returns_degraded_when_absent(
     assert resp["result"]["available"] is False
 
 
+def test_handler_degrades_when_no_kb_resolves(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    # The sibling test above covers "KB present, raw transcript missing". This
+    # one covers "no KB at all", which the handler used to answer with an
+    # internal error rather than the degraded envelope.
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.delenv("VOUCH_KB_PATH", raising=False)
+    monkeypatch.delenv("VOUCH_PROJECT_DIR", raising=False)
+    monkeypatch.setenv("VOUCH_CLAUDE_PROJECTS_DIR", str(tmp_path / "no-claude"))
+    monkeypatch.setenv("CODEX_HOME", str(tmp_path / "no-codex"))
+    from vouch.jsonl_server import handle_request
+
+    resp = handle_request({
+        "id": "3", "method": "kb.session_transcript",
+        "params": {"session_id": "11111111-1111-1111-1111-111111111111"},
+    })
+    assert resp["ok"] is True
+    assert resp["result"]["available"] is False
+    assert resp["result"]["observations"] == []
+
+
+def test_load_transcript_without_store_degrades(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setenv("VOUCH_CLAUDE_PROJECTS_DIR", str(tmp_path / "projects"))
+    out = transcript.load_transcript(None, "11111111-1111-1111-1111-111111111111")
+    assert out["available"] is False
+    assert out["observations"] == []
+
+
+def test_mcp_session_transcript_degrades_without_kb(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.chdir(tmp_path)
+    monkeypatch.delenv("VOUCH_KB_PATH", raising=False)
+    monkeypatch.delenv("VOUCH_PROJECT_DIR", raising=False)
+    monkeypatch.setenv("VOUCH_CLAUDE_PROJECTS_DIR", str(tmp_path / "no-claude"))
+    monkeypatch.setenv("CODEX_HOME", str(tmp_path / "no-codex"))
+    from vouch.server import kb_session_transcript
+
+    out = kb_session_transcript("11111111-1111-1111-1111-111111111111")
+    assert out["available"] is False
+    assert out["observations"] == []
+
+
 # --- Task 9: Codex parser -------------------------------------------------
 
 _CODEX_LINES = [