feat(P04): PAT lifecycle + nova auth login/revoke/status (REQ-342..344, C-7.3, security+cli)

---ci---
project: acdl
phase: 4
milestone: v1.28
status: execute
persona: cli-engineer
---

core/auth_store.py

@@ -0,0 +1,97 @@
+"""Nova credential store — ``~/.nova/credentials.json`` (C-7.3, REQ-344).
+
+Stores the OIDC token + PAT metadata (jti, exp, type) ONLY — **NOT the
+raw PAT** (C-7.3). The file is 0600. "Most recent wins" (D-226 Q5):
+``active_credential_jti`` points at the most-recently-stored credential.
+
+Shape::
+
+    {
+      "active_credential_jti": "<jti>",
+      "credentials": [
+        {"jti": ..., "type": "developer_pat"|"nova_oidc_token",
+         "exp": <epoch>, "token": "<oidc jwt>", "stored_at": <epoch>}
+      ]
+    }
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import stat
+import sys
+from pathlib import Path
+from typing import Optional
+
+
+def credentials_path() -> Path:
+    return Path(os.environ.get("NOVA_CREDENTIALS_FILE")
+                or os.path.expanduser("~/.nova/credentials.json"))
+
+
+def _emit_audit(event_type: str, **fields) -> None:
+    payload = {"event": event_type, **fields}
+    sys.stderr.write(json.dumps(payload, sort_keys=True) + "\n")
+    sys.stderr.flush()
+
+
+def store_credential(
+    jti: str,
+    cred_type: str,
+    exp: int,
+    oidc_token: str,
+    path: Optional[Path] = None,
+) -> None:
+    """Store an OIDC token + PAT metadata (NOT the raw PAT, C-7.3). 0600."""
+    p = path or credentials_path()
+    p.parent.mkdir(parents=True, exist_ok=True)
+    data = {"active_credential_jti": jti, "credentials": []}
+    if p.exists():
+        try:
+            data = json.loads(p.read_text())
+        except (OSError, json.JSONDecodeError):
+            data = {"active_credential_jti": jti, "credentials": []}
+    creds = data.get("credentials", []) or []
+    # Replace any existing entry with the same jti.
+    creds = [c for c in creds if c.get("jti") != jti]
+    import time
+    creds.append({
+        "jti": jti, "type": cred_type, "exp": exp,
+        "token": oidc_token, "stored_at": int(time.time()),
+    })
+    data["credentials"] = creds
+    data["active_credential_jti"] = jti
+    p.write_text(json.dumps(data, indent=2, sort_keys=True))
+    os.chmod(p, stat.S_IRUSR | stat.S_IWUSR)  # 0600
+    _emit_audit("auth.login", jti=jti, type=cred_type)
+
+
+def load_credentials(path: Optional[Path] = None) -> dict:
+    """Load the credentials file (or ``{}`` if absent)."""
+    p = path or credentials_path()
+    try:
+        return json.loads(p.read_text())
+    except (OSError, json.JSONDecodeError):
+        return {}
+
+
+def active_credential(path: Optional[Path] = None) -> Optional[dict]:
+    """Return the active credential dict (or ``None``)."""
+    data = load_credentials(path)
+    active_jti = data.get("active_credential_jti")
+    for c in data.get("credentials", []) or []:
+        if c.get("jti") == active_jti:
+            return c
+    return None
+
+
+def emit_status_audit(path: Optional[Path] = None) -> dict:
+    """Emit ``auth.status`` audit + return the credentials data."""
+    data = load_credentials(path)
+    _emit_audit("auth.status", active_jti=data.get("active_credential_jti"))
+    return data
+
+
+def emit_revoke_audit(jti: str) -> None:
+    _emit_audit("auth.revoke", jti=jti)