docs(milestone): complete v0.4-operator-tier — v0.1.9 tagged, milestone release, merged to main

v0.4 (Operator Tier — Cohort Dashboard + Auth + Postgres) milestone complete.

Phases:
  ✓ P0  pre-execution (planning)        → v0.1.6
  ✓ P1  operator foundation (Postgres+auth+VC migration) → v0.1.7
  ✓ P2  cohort dashboard + aggregation   → v0.1.8
  ✓ P3  final review + ship              → v0.1.9 (= v0.4 milestone release)

Requirements covered (8/8):
  REQ-MT-01 (Postgres store), REQ-MT-02 (aggregation pipeline),
  REQ-AUTH-01 (operator auth), REQ-DASH-01 (cohort dashboard),
  REQ-NFR-AUTH-01 (auth NFRs), REQ-NFR-MT-01 (Postgres-in-LXC),
  REQ-NFR-DASH-01 (k-anonymity ≥10), REQ-NFR-DASH-02 (freshness ≤24h)

Grill MUSTs honored (6/6): G-008, G-011, G-027, G-031, G-038, G-041

Tests: 317 pytest pass, 36 skip (Postgres-requiring), 0 fail; 17/17 vitest pass
Review: APPROVE_WITH_NOTES (6/6 personas, 0 P0, 8 P1+ carry-forward)
Audit: HEALTHY (reconstruction PASS, 8/8 REQ, 6/6 grill)

---ci---
project: praxis
phase: 3
milestone: v0.4
status: complete
phase_role: final
milestone_complete: true
milestone_merged_to_main: true
tag: v0.1.9
requirements:
  covered: [REQ-MT-01, REQ-MT-02, REQ-AUTH-01, REQ-DASH-01, REQ-NFR-AUTH-01, REQ-NFR-MT-01, REQ-NFR-DASH-01, REQ-NFR-DASH-02]
  partial: []
---/ci---

server/operator/failure_patterns.py

@@ -0,0 +1,44 @@
+"""GET /api/operator/failure-patterns — failure patterns view (TASK-08-03, D-053).
+
+Auth-gated. Returns failure pattern metrics: failure_mode frequency (cells
+with metric prefix `failure_mode:`) + branch outcome distribution (cells
+with metric prefix `branch:`). Weak-spot rubric criteria (mean < 3.0) are
+highlighted by the frontend. All k-anonymized.
+"""
+
+from __future__ import annotations
+
+import datetime as _dt
+
+from fastapi import APIRouter, Depends, Request
+
+from server.auth.dependencies import current_operator
+from server.auth.models import Operator
+from server.operator._common import (
+    ViewResponse,
+    all_recent_aggregates,
+    group_by_path,
+    require_pg_store,
+)
+
+router = APIRouter(prefix="/api/operator", tags=["operator-failure-patterns"])
+
+
+def _is_failure_metric(metric: str) -> bool:
+    return metric.startswith("failure_mode:") or metric.startswith("branch:")
+
+
+@router.get("/failure-patterns", response_model=ViewResponse)
+async def failure_patterns_view(
+    request: Request,
+    op: Operator = Depends(current_operator),
+) -> ViewResponse:
+    pg_store = await require_pg_store(request)
+    since = _dt.date.today() - _dt.timedelta(days=30)
+    rows = await all_recent_aggregates(pg_store, since)
+    failure_rows = [r for r in rows if _is_failure_metric(r.get("metric", ""))]
+    views, last_updated = group_by_path(failure_rows)
+    return ViewResponse(views=views, last_updated=last_updated)
+
+
+__all__ = ["router"]