Add GET /auth/api/check endpoint for unauthenticated user permission checks

Checks permissions for a user given by ?user=<UUID> query arg without
requiring a session cookie. No cookie is read or written, no DB writes.

- perm= query arg supported (same wildcard semantics as validate/forward)
- Returns valid bool + minimal ctx (user/org/role/permissions)
- Permissions are host-scoped via domain filtering, same as session_ctx
- 404 if UUID not found; valid=false if perm check fails (no 403)
- Add ApiCheckUserResponse struct to apistructs
- Add has_all_scopes() helper to permutil for scope-set-based checks

paskia/__main__.py

@@ -1,11 +1,13 @@
 import argparse
 import logging
 import os
+import sys
 
 import msgspec
 from fastapi_vue import server
 from fastapi_vue.hostutil import parse_endpoints
 
+from paskia._version import __version__
 from paskia.db.jsonl import load_readonly
 from paskia.util import startupbox
 from paskia.util.hostutil import (
@@ -74,7 +76,11 @@ def main():
 
     # Load stored config (read-only, no writes, no global state)
     db_path = os.environ.get("PASKIA_DB", f"{args.rp_id}.paskiadb")
+    try:
         config = load_readonly(db_path, rp_id=args.rp_id).config
+    except SystemExit as e:
+        print(f"🛑 Paskia {__version__} could not load")
+        sys.exit(str(e))
 
     # Override stored config with CLI args, or clear with empty string
     if args.rp_name is not None:

paskia/db/jsonl.py

@@ -41,11 +41,9 @@ class ReplayResult(msgspec.Struct, frozen=False):
     changes: int = 0
 
 
-class DatabaseError(Exception):
+class DatabaseError(ValueError):
     """Exception raised for database loading errors."""
 
-    pass
-
 
 def _replay_from_data(data: bytes, db_path: str) -> ReplayResult:
     """Replay database state from file data, using the last snapshot if available."""
@@ -61,14 +59,16 @@ def _replay_from_data(data: bytes, db_path: str) -> ReplayResult:
 
     # Replay change records after the snapshot
     lines = data[start_offset:].split(b"\n")
-    for line_num, raw in enumerate(lines, start=1):  # 1-based line numbering
+    for raw in lines:
         line = raw.strip()
         if not line:
             continue
         try:
             change = msgspec.json.decode(line, type=ChangeRecord)
         except msgspec.DecodeError as e:
-            raise DatabaseError(f"{resolved_path}:{line_num}: {e}")
+            raise DatabaseError(
+                f"{resolved_path}: {e}\n{line.decode(errors='replace')}"
+            )
         result.state = jsondiff.patch(result.state, change.diff, marshal=True)
         result.v = change.v
         result.ts = change.ts
@@ -88,19 +88,10 @@ def load_readonly(db_path: str, *, rp_id: str = "localhost") -> DB:
         return DB(config=Config(rp_id=rp_id))
 
     try:
-        with open(path, "rb") as f:
-            content = f.read()
+        content = path.read_bytes()
         r = _replay_from_data(content, str(path.resolve()))
         data_dict = r.state
         version = r.v
-    except OSError as e:
-        _logger.exception("Failed to load database")
-        raise SystemExit(f"{e}")
-    except (ValueError, msgspec.DecodeError, DatabaseError) as e:
-        raise SystemExit(f"{e}")
-    except Exception as e:
-        _logger.exception("Unexpected error loading database")
-        raise SystemExit(f"{e}")
 
         if not data_dict:
             return DB(config=Config(rp_id=rp_id))
@@ -109,8 +100,18 @@ def load_readonly(db_path: str, *, rp_id: str = "localhost") -> DB:
         apply_migrations_readonly(data_dict, version, MigrationCtx(rp_id=rp_id))
 
         # Decode to msgspec struct
-    db = msgspec.json.decode(msgspec.json.encode(data_dict), type=DB)
-    return db
+        try:
+            return msgspec.json.decode(msgspec.json.encode(data_dict), type=DB)
+        except msgspec.ValidationError as e:
+            raise DatabaseError(f"{path.resolve()}: {e}") from None
+    except OSError as e:
+        _logger.exception("Failed to load database")
+        raise SystemExit(f"{e}")
+    except (ValueError, msgspec.DecodeError) as e:
+        raise SystemExit(f"{e}")
+    except Exception as e:
+        _logger.exception("Unexpected error loading database")
+        raise SystemExit(f"{e}")
 
 
 class ChangeRecord(msgspec.Struct, omit_defaults=True, kw_only=True):

paskia/fastapi/api.py

@@ -1,6 +1,7 @@
 import logging
 from contextlib import suppress
 from datetime import UTC, datetime, timedelta
+from uuid import UUID
 
 from fastapi import (
     Depends,
@@ -20,8 +21,17 @@ from paskia.fastapi import authz, session, user
 from paskia.fastapi.response import MsgspecResponse
 from paskia.fastapi.session import AUTH_COOKIE, AUTH_COOKIE_NAME, get_client_ip
 from paskia.globals import passkey as global_passkey
-from paskia.util import hostutil, htmlutil, passphrase, userinfo
-from paskia.util.apistructs import ApiSettings, ApiTokenInfo, ApiValidateResponse
+from paskia.util import hostutil, htmlutil, passphrase, permutil, userinfo
+from paskia.util.apistructs import (
+    ApiCheckUserResponse,
+    ApiOrgContext,
+    ApiRoleContext,
+    ApiSessionContext,
+    ApiSettings,
+    ApiTokenInfo,
+    ApiUserContext,
+    ApiValidateResponse,
+)
 
 bearer_auth = HTTPBearer(auto_error=False)
 
@@ -109,6 +119,60 @@ async def validate_token(
     )
 
 
+@app.get("/check")
+async def check_user(
+    request: Request,
+    user_uuid: UUID = Query(..., alias="user"),
+    perm: list[str] = Query([]),
+):
+    """Check permissions for a user by UUID without requiring a session.
+
+    Query Params:
+    - user: UUID of the user to check.
+    - perm: repeated permission scope the user must possess (ALL required).
+
+    Returns 200 with valid=True/False and the user's effective permissions,
+    scoped to the requesting host (domain-restricted permissions are filtered).
+    Returns 404 if the user UUID does not exist.
+
+    No session cookie is read or written. Caller authentication is not required.
+    """
+    data = db.data()
+    try:
+        u = data.users[user_uuid]
+        role = u.role
+        org = role.org
+    except KeyError:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    host = hostutil.normalize_host(request.headers.get("host"))
+    org_perm_uuids = {p.uuid for p in org.permissions}
+
+    effective_perms = []
+    for perm_uuid in role.permission_set:
+        if perm_uuid not in org_perm_uuids:
+            continue
+        try:
+            p = data.permissions[perm_uuid]
+        except KeyError:
+            continue
+        if p.domain is not None and p.domain != host:
+            continue
+        effective_perms.append(p)
+
+    required = " ".join(perm).split()
+    effective_scopes = {p.scope for p in effective_perms}
+    valid = permutil.has_all_scopes(effective_scopes, required)
+
+    ctx = ApiSessionContext(
+        user=ApiUserContext(uuid=u.uuid, display_name=u.display_name, theme=u.theme),
+        org=ApiOrgContext(uuid=org.uuid, display_name=org.display_name),
+        role=ApiRoleContext(uuid=role.uuid, display_name=role.display_name),
+        permissions=sorted(effective_scopes),
+    )
+    return MsgspecResponse(ApiCheckUserResponse(valid=valid, ctx=ctx))
+
+
 @app.get("/forward")
 async def forward_authentication(
     request: Request,

paskia/util/apistructs.py

@@ -233,6 +233,13 @@ class ApiValidateResponse(msgspec.Struct):
     ctx: ApiSessionContext
 
 
+class ApiCheckUserResponse(msgspec.Struct):
+    """Response struct for check-user endpoint."""
+
+    valid: bool
+    ctx: ApiSessionContext
+
+
 class ApiAdminInfo(msgspec.Struct, kw_only=True):
     """Combined admin info response."""
 

paskia/util/permutil.py

@@ -6,7 +6,7 @@ from fnmatch import fnmatchcase
 from paskia.authsession import session_ctx
 from paskia.util.hostutil import normalize_host
 
-__all__ = ["has_any", "has_all", "session_context"]
+__all__ = ["has_any", "has_all", "has_all_scopes", "session_context"]
 
 
 def _match(perms: set[str], patterns: Sequence[str]):
@@ -36,6 +36,11 @@ def has_all(ctx, patterns: Sequence[str]) -> bool:
     return all(_match(_get_effective_scopes(ctx), patterns)) if ctx else False
 
 
+def has_all_scopes(scopes: set[str], patterns: Sequence[str]) -> bool:
+    """Check that a pre-computed scope set satisfies all required patterns."""
+    return all(_match(scopes, patterns)) if patterns else True
+
+
 async def session_context(auth: str | None, host: str | None = None):
     if not auth:
         return None