feat(exam): /api/exam template CRUD router (as-user RLS, E1 fix)

S4-5: new routers/exam/ package mounted at /api/exam (R5.1/E5, not under
/database/). Template CRUD with hybrid persistence (R5.2):

- POST/GET/GET{id}/PUT{id}/DELETE{id} /templates + PATCH /questions/{qid}
- Calls Supabase AS THE USER via SupabaseAnonClient.for_user (E1 fix), so the
  RLS in 72-exam-marker.sql is enforced; no service-role for user-facing ops.
- Institute resolved/validated via the user_institute_ids() SECURITY DEFINER
  RPC (institute_memberships is deny-all as-user per E4); client-supplied
  institute_id is validated, never trusted (R5.5).
- Ownership pre-checked before writes (E2); out-of-scope ids read back as 404
  under RLS (IDOR-safe). Soft-delete archives, never hard-deletes.
- PUT full-replace preserves client UUIDs as Neo4j join keys (spec §2).
- eb_exams.exam_code denormalised via a documented service-role catalogue
  lookup (eb_exams is shared reference data, deny-all as-user per E4).

Unit tests cover auth, CRUD, ownership/IDOR, institute validation, soft-delete.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

routers/exam/schemas.py

@@ -0,0 +1,104 @@
+"""Pydantic request/response models for the /api/exam/ router (S4-5).
+
+Templates are saved from the canvas with a full-replace PUT (R5.2): the client owns
+stable UUIDs for questions / response areas / boundaries so the Supabase ids line up
+with the Neo4j join keys (exam_questions.id ↔ Question|Part.uuid_string,
+exam_response_areas.id ↔ Region.uuid_string — see spec §2). Granular mark-scheme edits
+go through PATCH /api/exam/questions/{qid}.
+
+Models mirror the columns in volumes/db/cc/72-exam-marker.sql. They are intentionally
+permissive (most fields optional) so the canvas can round-trip partial state during
+authoring without the API rejecting work-in-progress.
+"""
+from __future__ import annotations
+
+from typing import Any, Dict, List, Literal, Optional
+
+from pydantic import BaseModel, Field
+
+
+# ─── Templates ─────────────────────────────────────────────────────────────────
+
+class CreateTemplateRequest(BaseModel):
+    title: str
+    subject: Optional[str] = None
+    # Catalogue paper (eb_exams) the template maps, when chosen from the catalogue (R2.2).
+    exam_id: Optional[str] = None
+    # Denormalised onto the template for the Neo4j join (eb_exams.exam_code ↔ ExamPaper.exam_code).
+    # If exam_id is given but exam_code is omitted, the API resolves it from the catalogue.
+    exam_code: Optional[str] = None
+    # Uploaded PDF (files.id) for an ad-hoc paper (R2.2).
+    source_file_id: Optional[str] = None
+    page_count: Optional[int] = None
+    # Active institute (R1.4/R5.5). Validated against the caller's memberships; never trusted
+    # as the authorization signal. Optional when the caller belongs to exactly one institute.
+    institute_id: Optional[str] = None
+
+
+class UpdateTemplateMetaRequest(BaseModel):
+    """Template-level fields that a full-replace PUT may also update alongside the canvas."""
+    title: Optional[str] = None
+    subject: Optional[str] = None
+    page_count: Optional[int] = None
+    status: Optional[Literal["draft", "ready", "archived"]] = None
+
+
+# ─── Canvas entities (children of a template) ────────────────────────────────────
+
+class QuestionPayload(BaseModel):
+    # Client-supplied stable UUID (== Neo4j Question|Part.uuid_string). Optional on first save.
+    id: Optional[str] = None
+    parent_id: Optional[str] = None
+    label: str
+    order: int = 0
+    max_marks: float = 0
+    answer_type: Optional[Literal["written", "mcq", "short", "diagram"]] = None
+    mcq_options: Optional[Any] = None
+    mark_scheme: Dict[str, Any] = Field(default_factory=dict)
+    is_container: bool = False
+    spec_ref: Optional[str] = None
+
+
+class ResponseAreaPayload(BaseModel):
+    id: Optional[str] = None  # == Neo4j Region.uuid_string
+    question_id: str
+    page: int
+    bounds: Dict[str, Any]  # {x,y,w,h}
+    kind: Literal["response", "context"]
+    response_form: Optional[
+        Literal["lines", "answer-box", "working", "diagram", "tick-boxes", "table", "blanks"]
+    ] = None
+    source: Literal["manual", "ai"] = "manual"
+    confirmed: bool = True
+    confidence: Optional[float] = None
+
+
+class BoundaryPayload(BaseModel):
+    id: Optional[str] = None
+    question_id: Optional[str] = None
+    label: Optional[str] = None
+    page_index: int
+    y: float
+    bounds: Optional[Dict[str, Any]] = None
+    source: Literal["manual", "ai"] = "manual"
+    confirmed: bool = True
+
+
+class TemplateReplaceRequest(BaseModel):
+    """Full-replace canvas save (R5.2 primary path). All children are replaced wholesale."""
+    meta: Optional[UpdateTemplateMetaRequest] = None
+    questions: List[QuestionPayload] = Field(default_factory=list)
+    response_areas: List[ResponseAreaPayload] = Field(default_factory=list)
+    boundaries: List[BoundaryPayload] = Field(default_factory=list)
+
+
+class PatchQuestionRequest(BaseModel):
+    """Incremental mark-scheme / spec-ref edit (R5.2 granular path)."""
+    label: Optional[str] = None
+    order: Optional[int] = None
+    max_marks: Optional[float] = None
+    answer_type: Optional[Literal["written", "mcq", "short", "diagram"]] = None
+    mcq_options: Optional[Any] = None
+    mark_scheme: Optional[Dict[str, Any]] = None
+    is_container: Optional[bool] = None
+    spec_ref: Optional[str] = None