feat(db): track API endpoint dimension on usage_history

Add an `endpoint` column to `usage_history` (migration 103) so the proxy
records which API entry point a request came through — typically
`/v1/chat/completions`, `/v1/messages`, or `/v1/responses`. Every
`saveRequestUsage(...)` call site in `open-sse/handlers/chatCore.ts`
(success, stream, failure) and the codex-responses-ws route now plumbs
the endpoint through, and a new `getEndpointUsageRows(...)` analytics
query in `src/lib/db/usageAnalytics.ts` aggregates per
endpoint × provider × model with NULL → 'unknown' folding for backward
compatibility with rows from before the migration.

The aggregation reads directly from `usage_history` (matching the
`getAutoRoutingVariantBreakdown` pattern) so the existing unified-source
CTE — and the `daily_usage_summary` rollup it joins — stay untouched.

TDD: tests/unit/usage-endpoint-dimension.test.ts covers persistence
round-trip, NULL fallback, and the sinceIso filter (3/3 passing).

Co-authored-by: toanalien <toanalien@gmail.com>
Inspired-by: https://github.com/decolua/9router/pull/152

tests/unit/usage-endpoint-dimension.test.ts

@@ -0,0 +1,125 @@
+/**
+ * Ported feature regression — decolua/9router#152 (thanks @toanalien).
+ *
+ * Covers the new `endpoint` column on usage_history + getEndpointUsageRows()
+ * aggregation. Asserts: persistence round-trip, NULL → 'unknown' folding,
+ * per-endpoint grouping, sinceIso filter.
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+const TEST_DATA_DIR = fs.mkdtempSync(path.join(os.tmpdir(), "omniroute-usage-endpoint-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+
+const core = await import("../../src/lib/db/core.ts");
+const usageHistory = await import("../../src/lib/usage/usageHistory.ts");
+const usageAnalytics = await import("../../src/lib/db/usageAnalytics.ts");
+
+async function resetStorage() {
+  core.resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+  fs.mkdirSync(TEST_DATA_DIR, { recursive: true });
+  usageHistory.clearPendingRequests();
+}
+
+test.beforeEach(async () => {
+  await resetStorage();
+});
+
+test.after(() => {
+  core.resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+test("saveRequestUsage persists endpoint and getEndpointUsageRows groups by endpoint", async () => {
+  await usageHistory.saveRequestUsage({
+    provider: "openai",
+    model: "gpt-4o-mini",
+    tokens: { input: 10, output: 5 },
+    success: true,
+    latencyMs: 100,
+    timestamp: new Date().toISOString(),
+    endpoint: "/v1/chat/completions",
+  });
+  await usageHistory.saveRequestUsage({
+    provider: "openai",
+    model: "gpt-4o-mini",
+    tokens: { input: 20, output: 8 },
+    success: true,
+    latencyMs: 200,
+    timestamp: new Date().toISOString(),
+    endpoint: "/v1/chat/completions",
+  });
+  await usageHistory.saveRequestUsage({
+    provider: "anthropic",
+    model: "claude-sonnet-4",
+    tokens: { input: 30, output: 12 },
+    success: true,
+    latencyMs: 300,
+    timestamp: new Date().toISOString(),
+    endpoint: "/v1/messages",
+  });
+
+  const rows = usageAnalytics.getEndpointUsageRows();
+  const byKey = new Map(rows.map((r) => [`${r.endpoint}|${r.provider}|${r.model}`, r]));
+
+  const chat = byKey.get("/v1/chat/completions|openai|gpt-4o-mini");
+  assert.ok(chat, "expected /v1/chat/completions row");
+  assert.equal(chat.requests, 2);
+  assert.equal(chat.promptTokens, 30);
+  assert.equal(chat.completionTokens, 13);
+
+  const messages = byKey.get("/v1/messages|anthropic|claude-sonnet-4");
+  assert.ok(messages, "expected /v1/messages row");
+  assert.equal(messages.requests, 1);
+  assert.equal(messages.promptTokens, 30);
+});
+
+test("getEndpointUsageRows folds NULL endpoint into 'unknown' bucket (backward compat)", async () => {
+  // Legacy entry: no endpoint field set → stored as NULL.
+  await usageHistory.saveRequestUsage({
+    provider: "openai",
+    model: "gpt-4o-mini",
+    tokens: { input: 5, output: 5 },
+    success: true,
+    latencyMs: 50,
+    timestamp: new Date().toISOString(),
+  });
+
+  const rows = usageAnalytics.getEndpointUsageRows();
+  const unknown = rows.find((r) => r.endpoint === "unknown");
+  assert.ok(unknown, "NULL endpoint should fold into 'unknown'");
+  assert.equal(unknown.requests, 1);
+});
+
+test("getEndpointUsageRows honors sinceIso filter", async () => {
+  const old = new Date(Date.now() - 24 * 60 * 60 * 1000).toISOString();
+  const recent = new Date().toISOString();
+  await usageHistory.saveRequestUsage({
+    provider: "openai",
+    model: "gpt-4o-mini",
+    tokens: { input: 5, output: 5 },
+    success: true,
+    latencyMs: 50,
+    timestamp: old,
+    endpoint: "/v1/chat/completions",
+  });
+  await usageHistory.saveRequestUsage({
+    provider: "openai",
+    model: "gpt-4o-mini",
+    tokens: { input: 5, output: 5 },
+    success: true,
+    latencyMs: 50,
+    timestamp: recent,
+    endpoint: "/v1/chat/completions",
+  });
+
+  const sinceIso = new Date(Date.now() - 60 * 60 * 1000).toISOString();
+  const rows = usageAnalytics.getEndpointUsageRows({ sinceIso });
+  const chat = rows.find((r) => r.endpoint === "/v1/chat/completions");
+  assert.ok(chat);
+  assert.equal(chat.requests, 1, "only the recent row should be counted");
+});