fix(router): honor stats filePath

src/router/config/parseRouterConfig.ts

@@ -535,7 +535,20 @@ function parseStats(
     modelConfig,
     diagnostics,
   );
-  return { enabled, modelPricing, baselineModel };
+  let filePath: string | undefined;
+  if (raw.filePath !== undefined) {
+    if (typeof raw.filePath === "string") {
+      filePath = raw.filePath.trim().length > 0 ? raw.filePath : undefined;
+    } else {
+      diagnostics.push({
+        code: "ROUTER_STATS_FILE_PATH_INVALID",
+        severity: "fatal",
+        path: "router.stats.filePath",
+        message: "filePath must be a string.",
+      });
+    }
+  }
+  return { enabled, modelPricing, filePath, baselineModel };
 }
 
 function parseCustomRouter(

src/router/config/schema.ts

@@ -55,7 +55,7 @@ export const DEFAULT_SUBAGENT_MAX_TOKENS = 48000;
 export type RouterStatsConfig = {
   enabled: boolean;
   modelPricing?: Record<string, { input?: number; output?: number; cacheRead?: number }>;
-  /** Override the default ~/.pilotdeck/router/stats.json path (useful for tests). */
+  /** Override the default ~/.pilotdeck/router/stats.jsonl path (useful for tests). */
   filePath?: string;
   /** Provider/model ref used as the "no-router" baseline for savedCost calculation. */
   baselineModel?: { provider: string; model: string };

src/router/stats/TokenStatsCollector.ts

@@ -68,12 +68,13 @@ export class TokenStatsCollector {
     this.baselineModel = config?.baselineModel;
 
     if (this.enabled) {
-      const routerDir = config?.filePath
-        ? path.dirname(config.filePath)
+      const filePath = config?.filePath?.trim() ? config.filePath : undefined;
+      const routerDir = filePath
+        ? path.dirname(filePath)
         : path.join(resolvePilotHome(), "router");
       try { fs.mkdirSync(routerDir, { recursive: true }); } catch { /* ok */ }
 
-      this.jsonlPath = path.join(routerDir, "stats.jsonl");
+      this.jsonlPath = filePath ?? path.join(routerDir, "stats.jsonl");
 
       // One-time migration: old JSON formats → JSONL
       migrateJsonToJsonl(routerDir, this.jsonlPath);

tests/router-stats-filepath.test.ts

@@ -0,0 +1,112 @@
+import assert from "node:assert/strict";
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+import test from "node:test";
+import type { ModelConfig } from "../src/model/index.js";
+import { parseRouterConfig } from "../src/router/config/parseRouterConfig.js";
+import { TokenStatsCollector } from "../src/router/stats/TokenStatsCollector.js";
+
+const modelConfig: ModelConfig = { providers: {} };
+
+function observeOneRecord(collector: TokenStatsCollector): void {
+  collector.observe({
+    sessionId: "session-1",
+    scenarioType: "default",
+    resolvedFrom: "scenario",
+    provider: "openai",
+    model: "gpt-4o-mini",
+    usage: {
+      inputTokens: 10,
+      outputTokens: 5,
+    },
+    startedAt: "2026-06-23T00:00:00.000Z",
+    endedAt: "2026-06-23T00:00:01.000Z",
+  });
+}
+
+test("parseRouterConfig preserves router.stats.filePath", () => {
+  const filePath = "/tmp/custom-router-stats.jsonl";
+  const result = parseRouterConfig(
+    {
+      stats: {
+        enabled: true,
+        filePath,
+      },
+    },
+    modelConfig,
+  );
+
+  assert.deepEqual(result.diagnostics, []);
+  assert.equal(result.config?.stats?.filePath, filePath);
+});
+
+test("parseRouterConfig treats blank router.stats.filePath as unset", () => {
+  const result = parseRouterConfig(
+    {
+      stats: {
+        enabled: true,
+        filePath: "",
+      },
+    },
+    modelConfig,
+  );
+
+  assert.deepEqual(result.diagnostics, []);
+  assert.equal(result.config?.stats?.filePath, undefined);
+});
+
+test("TokenStatsCollector writes to the configured stats file path", () => {
+  const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "pilotdeck-stats-"));
+  const customPath = path.join(tempDir, "custom-name.jsonl");
+  const defaultPath = path.join(tempDir, "stats.jsonl");
+
+  try {
+    const collector = new TokenStatsCollector({
+      enabled: true,
+      filePath: customPath,
+    });
+
+    observeOneRecord(collector);
+    collector.dispose();
+
+    assert.equal(fs.existsSync(customPath), true);
+    assert.equal(fs.existsSync(defaultPath), false);
+
+    const [line] = fs.readFileSync(customPath, "utf-8").trim().split("\n");
+    const record = JSON.parse(line!);
+    assert.equal(record.sessionId, "session-1");
+  } finally {
+    fs.rmSync(tempDir, { recursive: true, force: true });
+  }
+});
+
+test("TokenStatsCollector falls back to the default path for blank filePath", () => {
+  const tempHome = fs.mkdtempSync(path.join(os.tmpdir(), "pilotdeck-home-"));
+  const previousPilotHome = process.env.PILOT_HOME;
+
+  try {
+    process.env.PILOT_HOME = tempHome;
+    const collector = new TokenStatsCollector({
+      enabled: true,
+      filePath: "",
+    });
+
+    observeOneRecord(collector);
+    collector.dispose();
+
+    const defaultPath = path.join(tempHome, "router", "stats.jsonl");
+    assert.equal(fs.existsSync(defaultPath), true);
+
+    const [line] = fs.readFileSync(defaultPath, "utf-8").trim().split("\n");
+    const record = JSON.parse(line!);
+    assert.equal(record.sessionId, "session-1");
+  } finally {
+    if (previousPilotHome === undefined) {
+      delete process.env.PILOT_HOME;
+    } else {
+      process.env.PILOT_HOME = previousPilotHome;
+    }
+    fs.rmSync(tempHome, { recursive: true, force: true });
+  }
+});