feat: export aggregate Prometheus metrics

packages/casan-control-panel/backend/src/telemetry/telemetry.controller.ts

@@ -1,6 +1,6 @@
 // Read-only Ops Console API. Every handler returns the standard ok() envelope. No writes,
 // no auth (loopback-bound, "Đọc ≠ Ghi"); management/RBAC is Plan-13 Track 2/3 (future).
-import { Controller, Get, Inject, Param, Query, Req, Res } from '@nestjs/common';
+import { Controller, Get, Header, Inject, Param, Query, Req, Res } from '@nestjs/common';
 import type { Request, Response } from 'express';
 import { ok } from '../common/api-response.js';
 import { TelemetryService } from './telemetry.service.js';
@@ -16,6 +16,14 @@ export class TelemetryController {
     return ok(this.svc.overview());
   }
 
+  // Production reverse proxy policy must restrict this aggregate-only endpoint
+  // to the monitoring network / service account.
+  @Get('metrics')
+  @Header('Content-Type', 'text/plain; version=0.0.4; charset=utf-8')
+  metrics() {
+    return this.svc.prometheusMetrics();
+  }
+
   @Get('runs')
   runs(@Query('limit') limit?: string) {
     const n = Math.min(Math.max(Number(limit) || 50, 1), 500);

packages/casan-control-panel/backend/src/telemetry/telemetry.service.ts

@@ -263,6 +263,51 @@ export class TelemetryService {
     };
   }
 
+  // Prometheus exposition is deliberately aggregate-only. Do not add trace IDs,
+  // actor/tenant identifiers, prompts, filenames or evidence content as labels:
+  // those would turn an operations endpoint into a data-exfiltration path.
+  prometheusMetrics() {
+    const overview = this.overview();
+    const totals = overview.totals;
+    const lines = [
+      '# HELP casan_telemetry_stale Whether the primary telemetry feed is stale (1=true).',
+      '# TYPE casan_telemetry_stale gauge',
+      `casan_telemetry_stale ${overview.stale ? 1 : 0}`,
+      '# HELP casan_telemetry_age_seconds Age of the primary telemetry feed in seconds.',
+      '# TYPE casan_telemetry_age_seconds gauge',
+      `casan_telemetry_age_seconds ${overview.age_s ?? -1}`,
+      '# HELP casan_runs_total Number of telemetry records retained by CASAN.',
+      '# TYPE casan_runs_total gauge',
+      `casan_runs_total ${totals.runs}`,
+      '# HELP casan_failures_total Number of retained failed telemetry records.',
+      '# TYPE casan_failures_total gauge',
+      `casan_failures_total ${totals.failures}`,
+      '# HELP casan_cost_usd_total Aggregate estimated CASAN execution cost in USD.',
+      '# TYPE casan_cost_usd_total gauge',
+      `casan_cost_usd_total ${totals.total_cost}`,
+      '# HELP casan_provider_tokens_total Aggregate provider token usage.',
+      '# TYPE casan_provider_tokens_total gauge',
+      `casan_provider_tokens_total ${totals.provider_tokens}`,
+      '# HELP casan_security_blocks_total H4 security verdicts blocked.',
+      '# TYPE casan_security_blocks_total gauge',
+      `casan_security_blocks_total ${overview.harness_signals['H4-security'].blocked}`,
+      '# HELP casan_governance_denials_total H5 governance decisions denied.',
+      '# TYPE casan_governance_denials_total gauge',
+      `casan_governance_denials_total ${overview.harness_signals['H5-governance'].denied}`,
+      '# HELP casan_tool_denials_total Tool registry decisions denied.',
+      '# TYPE casan_tool_denials_total gauge',
+      `casan_tool_denials_total ${totals.tool_denies}`,
+      '# HELP casan_action_blocks_total Governed action gate block outcomes.',
+      '# TYPE casan_action_blocks_total gauge',
+      `casan_action_blocks_total ${totals.action_blocks}`,
+      '# HELP casan_critical_incidents_total Retained critical incident records.',
+      '# TYPE casan_critical_incidents_total gauge',
+      `casan_critical_incidents_total ${overview.harness_signals.incidents.critical}`,
+      '',
+    ];
+    return lines.join('\n');
+  }
+
   runs(limit = 50) {
     const metrics = readJsonl(PATHS.metrics);
     return { ...this.freshness(), count: metrics.length, runs: recent(metrics, limit) };

packages/casan-control-panel/backend/test/telemetry.test.ts

@@ -40,6 +40,15 @@ test('overview() returns real aggregated shape, never throws on the repo state',
   assert.ok(o.audit_chain.records >= 0);
 });
 
+test('prometheusMetrics() exports aggregate-safe operational metrics only', () => {
+  const metrics = new TelemetryService().prometheusMetrics();
+  assert.match(metrics, /^# HELP casan_telemetry_stale/m);
+  assert.match(metrics, /^casan_runs_total \d+/m);
+  assert.match(metrics, /^casan_security_blocks_total \d+/m);
+  assert.match(metrics, /^casan_governance_denials_total \d+/m);
+  assert.doesNotMatch(metrics, /trace_id|tenant|prompt|evidence/i);
+});
+
 test('security()/governance()/cost() return objects with expected keys', () => {
   const svc = new TelemetryService();
   assert.ok(typeof (svc.security() as any).by_status === 'object');