feat(Day 49 phase 1.5): GET /v1/doctrines/{id} for dossier expand

Adds per-doctrine details endpoint for the dossier click-to-expand
UX. Returns name_he, elements, exceptions, statute_refs (full),
leading_cases (full), and pending_review flag. Keywords stay
internal — they're a tuning surface, not user-facing.

CRITICAL: registered AFTER /v1/doctrines/catalog so the static
path matches first. FastAPI routes match in registration order,
so /v1/doctrines/{doctrine_id} placed earlier would shadow catalog.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tau_rag/api/fastapi_app.py

@@ -22620,3 +22620,41 @@ def doctrines_catalog_public():  # type: ignore
         return JSONResponse(status_code=500, content={
             "ok": False, "error": f"{type(e).__name__}: {e}"
         })
+
+
+@app.get("/v1/doctrines/{doctrine_id}")
+def doctrines_get_one(doctrine_id: str):  # type: ignore
+    """Day 49 — full per-doctrine details for the dossier expand-on-click.
+
+    Returns name_he, elements, exceptions, statute_refs, all leading_cases,
+    and the `pending_lawyer_review` flag. Keywords stay internal —
+    they're a tuning surface, not user-facing.
+
+    NOTE: must be registered AFTER /v1/doctrines/catalog so the
+    static path wins over the dynamic match.
+    """
+    try:
+        from ..intelligence.doctrine_classifier import load_doctrine_catalog
+        cat = load_doctrine_catalog()
+        idx = {d["id"]: d for d in cat.get("doctrines", [])}
+        doc = idx.get(doctrine_id)
+        if not doc:
+            return JSONResponse(status_code=404, content={
+                "ok": False, "reason": "doctrine_not_found",
+            })
+        return {
+            "ok":               True,
+            "id":               doc.get("id"),
+            "name_he":          doc.get("name_he"),
+            "name_en":          doc.get("name_en"),
+            "domain":           doc.get("domain"),
+            "elements":         doc.get("elements") or [],
+            "exceptions":       doc.get("exceptions") or [],
+            "statute_refs":     doc.get("statute_refs") or [],
+            "leading_cases":    doc.get("leading_cases") or [],
+            "pending_review":   bool(doc.get("_pending_lawyer_review")),
+        }
+    except Exception as e:
+        return JSONResponse(status_code=500, content={
+            "ok": False, "error": f"{type(e).__name__}: {e}"
+        })