diff --git a/src/app/api/tools/traffic-inspector/sessions/[id]/requests/route.ts b/src/app/api/tools/traffic-inspector/sessions/[id]/requests/route.ts
new file mode 100644
index 0000000000..95dd5fa0c3
--- /dev/null
+++ b/src/app/api/tools/traffic-inspector/sessions/[id]/requests/route.ts
@@ -0,0 +1,62 @@
+/**
+ * POST /api/tools/traffic-inspector/sessions/[id]/requests — persist a live snapshot entry
+ *
+ * Accepts a JSON-encoded InterceptedRequest payload and appends it to the
+ * session request log, atomically incrementing request_count. Returns the
+ * assigned seq number so the caller can confirm persistence order.
+ *
+ * LOCAL_ONLY enforced by routeGuard at the /api/tools/ prefix level.
+ *
+ * Part of R5-5 (backend half): the frontend hook (F3 / useSessionRecorder.ts)
+ * is the corresponding caller that POSTs snapshots here on stop().
+ */
+
+import { buildErrorBody, sanitizeErrorMessage } from "@omniroute/open-sse/utils/error.ts";
+import { InspectorSessionRequestAppendSchema } from "@/shared/schemas/inspector";
+import { getSession, appendSessionRequest } from "@/lib/db/inspectorSessions";
+
+interface Params {
+  params: Promise<{ id: string }>;
+}
+
+export async function POST(request: Request, { params }: Params): Promise<Response> {
+  const { id } = await params;
+
+  // Verify session exists before attempting to append
+  const session = getSession(id);
+  if (!session) {
+    return new Response(JSON.stringify(buildErrorBody(404, "Session not found")), {
+      status: 404,
+      headers: { "content-type": "application/json" },
+    });
+  }
+
+  let body: unknown;
+  try {
+    body = await request.json();
+  } catch {
+    return new Response(JSON.stringify(buildErrorBody(400, "Invalid JSON body")), {
+      status: 400,
+      headers: { "content-type": "application/json" },
+    });
+  }
+
+  const parsed = InspectorSessionRequestAppendSchema.safeParse(body);
+  if (!parsed.success) {
+    return new Response(
+      JSON.stringify(buildErrorBody(400, parsed.error.issues[0]?.message ?? "Validation error")),
+      { status: 400, headers: { "content-type": "application/json" } }
+    );
+  }
+
+  try {
+    const seq = appendSessionRequest(id, parsed.data.payload);
+    return Response.json({ seq }, { status: 201 });
+  } catch (err) {
+    const msg = sanitizeErrorMessage(err);
+    return new Response(
+      JSON.stringify(buildErrorBody(500, msg || "Failed to append session request")),
+      { status: 500, headers: { "content-type": "application/json" } }
+    );
+  }
+}
diff --git a/src/lib/db/inspectorSessions.ts b/src/lib/db/inspectorSessions.ts
index aae84257b5..faaee6081b 100644
--- a/src/lib/db/inspectorSessions.ts
+++ b/src/lib/db/inspectorSessions.ts
@@ -77,8 +77,9 @@ export function getSession(id: string): InspectorSessionRow | null {
   return row ? mapSessionRow(row) : null;
 }
 
-export function appendSessionRequest(sessionId: string, payload: string): void {
+export function appendSessionRequest(sessionId: string, payload: string): number {
   const db = getDbInstance();
+  let insertedSeq = 0;
 
   const runTransaction = db.transaction(() => {
     // Get next seq atomically within transaction
@@ -97,9 +98,12 @@ export function appendSessionRequest(sessionId: string, payload: string): void {
     db.prepare(
       "UPDATE inspector_sessions SET request_count = request_count + 1 WHERE id = ?"
     ).run(sessionId);
+
+    insertedSeq = nextSeq;
   });
 
   runTransaction();
+  return insertedSeq;
 }
 
 export function getSessionRequests(sessionId: string): Array<{ seq: number; payload: string }> {
diff --git a/src/shared/schemas/inspector.ts b/src/shared/schemas/inspector.ts
index 6fb3e59f9a..a474d4362b 100644
--- a/src/shared/schemas/inspector.ts
+++ b/src/shared/schemas/inspector.ts
@@ -32,6 +32,11 @@ export const InspectorAnnotationPutSchema = z.object({
   annotation: z.string().max(10_000),
 });
 
+// 1 MB cap — matches INSPECTOR_MAX_BODY_KB constant
+export const InspectorSessionRequestAppendSchema = z.object({
+  payload: z.string().max(1_048_576),
+});
+
 export const InspectorListQuerySchema = z.object({
   profile: z.enum(["llm", "custom", "all"]).optional(),
   host: z.string().optional(),
diff --git a/tests/integration/traffic-inspector-session-requests.test.ts b/tests/integration/traffic-inspector-session-requests.test.ts
new file mode 100644
index 0000000000..d0b9bcb14e
--- /dev/null
+++ b/tests/integration/traffic-inspector-session-requests.test.ts
@@ -0,0 +1,137 @@
+/**
+ * Integration tests: POST /api/tools/traffic-inspector/sessions/[id]/requests
+ *
+ * Tests snapshot persistence: seq increments, request_count sync, validation, 404.
+ */
+
+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-ti-session-requests-"));
+process.env.DATA_DIR = TEST_DATA_DIR;
+
+const { resetDbInstance, getDbInstance } = await import("../../src/lib/db/core.ts");
+
+async function resetStorage() {
+  resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+  fs.mkdirSync(TEST_DATA_DIR, { recursive: true });
+  getDbInstance();
+}
+
+const sessionsRoute = await import(
+  "../../src/app/api/tools/traffic-inspector/sessions/route.ts"
+);
+const sessionDetailRoute = await import(
+  "../../src/app/api/tools/traffic-inspector/sessions/[id]/route.ts"
+);
+const sessionRequestsRoute = await import(
+  "../../src/app/api/tools/traffic-inspector/sessions/[id]/requests/route.ts"
+);
+
+async function createSession(name?: string): Promise<string> {
+  const res = await sessionsRoute.POST(
+    new Request("http://localhost/api/tools/traffic-inspector/sessions", {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: JSON.stringify(name !== undefined ? { name } : {}),
+    })
+  );
+  const body = (await res.json()) as { id: string };
+  return body.id;
+}
+
+async function postRequest(sessionId: string, payload: string): Promise<Response> {
+  return sessionRequestsRoute.POST(
+    new Request("http://localhost/", {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: JSON.stringify({ payload }),
+    }),
+    { params: Promise.resolve({ id: sessionId }) }
+  );
+}
+
+test.beforeEach(async () => {
+  await resetStorage();
+});
+
+test.after(() => {
+  resetDbInstance();
+  fs.rmSync(TEST_DATA_DIR, { recursive: true, force: true });
+});
+
+test("POST /sessions/[id]/requests: seq increments 1, 2, 3", async () => {
+  const id = await createSession("seq-test");
+
+  const r1 = await postRequest(id, JSON.stringify({ note: "first" }));
+  assert.equal(r1.status, 201);
+  const b1 = (await r1.json()) as { seq: number };
+  assert.equal(b1.seq, 1);
+
+  const r2 = await postRequest(id, JSON.stringify({ note: "second" }));
+  assert.equal(r2.status, 201);
+  const b2 = (await r2.json()) as { seq: number };
+  assert.equal(b2.seq, 2);
+
+  const r3 = await postRequest(id, JSON.stringify({ note: "third" }));
+  assert.equal(r3.status, 201);
+  const b3 = (await r3.json()) as { seq: number };
+  assert.equal(b3.seq, 3);
+});
+
+test("POST /sessions/[id]/requests: GET session reflects requestCount === 3", async () => {
+  const id = await createSession("count-test");
+
+  await postRequest(id, "payload-1");
+  await postRequest(id, "payload-2");
+  await postRequest(id, "payload-3");
+
+  const getRes = await sessionDetailRoute.GET(new Request("http://localhost/"), {
+    params: Promise.resolve({ id }),
+  });
+  assert.equal(getRes.status, 200);
+  const body = (await getRes.json()) as { session: { request_count: number } };
+  assert.equal(body.session.request_count, 3);
+});
+
+test("POST /sessions/[id]/requests: invalid body returns 400", async () => {
+  const id = await createSession("validation-test");
+
+  // Missing `payload` field
+  const res = await sessionRequestsRoute.POST(
+    new Request("http://localhost/", {
+      method: "POST",
+      headers: { "content-type": "application/json" },
+      body: JSON.stringify({ not_payload: "oops" }),
+    }),
+    { params: Promise.resolve({ id }) }
+  );
+  assert.equal(res.status, 400);
+});
+
+test("POST /sessions/[id]/requests: payload exceeding 1MB cap returns 400", async () => {
+  const id = await createSession("size-cap-test");
+
+  // Exceed 1_048_576 bytes
+  const oversized = "x".repeat(1_048_577);
+  const res = await postRequest(id, oversized);
+  assert.equal(res.status, 400);
+});
+
+test("POST /sessions/[id]/requests: non-existent session id returns 404", async () => {
+  const res = await postRequest("00000000-0000-4000-8000-000000000000", "some-payload");
+  assert.equal(res.status, 404);
+});
+
+test("POST /sessions/[id]/requests: error response does not leak stack trace", async () => {
+  // POST to non-existent session — exercises the 404 path error body
+  const res = await postRequest("00000000-0000-4000-8000-000000000099", "data");
+  assert.equal(res.status, 404);
+  const body = await res.json() as { error?: { message?: string } };
+  const msg = body?.error?.message ?? "";
+  assert.ok(!msg.includes("at /"), "should not contain stack trace");
+});