diff --git a/apps/server/src/lane-map.ts b/apps/server/src/lane-map.ts
new file mode 100644
index 0000000..88e0e81
--- /dev/null
+++ b/apps/server/src/lane-map.ts
@@ -0,0 +1,30 @@
+import { laneDevices, type Db } from "@parking/db";
+
+// Resolves a device instance id (lane_devices.id) to its lane number.
+//
+// Device pushes/events carry the `lane_devices` id (which device fired), not a
+// lane. The event log wants the lane, so we keep a small in-memory id->lane map
+// rebuilt from the DB at startup and refreshed whenever assignments change
+// (assign/unassign). It's tiny (one row per device) and read on the hot path of
+// every input event, so a cached map beats a per-event DB lookup.
+export class LaneMap {
+  readonly #db: Db;
+  #byDeviceId = new Map<string, number>();
+
+  constructor(db: Db) {
+    this.#db = db;
+  }
+
+  /** (Re)load the id->lane map from the lane_devices table. */
+  refresh(): void {
+    const rows = this.#db.select().from(laneDevices).all();
+    const next = new Map<string, number>();
+    for (const r of rows) next.set(r.id, r.lane);
+    this.#byDeviceId = next;
+  }
+
+  /** Lane for a device instance id, or null if the device isn't known. */
+  laneFor(deviceId: string): number | null {
+    return this.#byDeviceId.get(deviceId) ?? null;
+  }
+}
diff --git a/apps/server/src/routes/setup.ts b/apps/server/src/routes/setup.ts
index 5b27379..50d65d6 100644
--- a/apps/server/src/routes/setup.ts
+++ b/apps/server/src/routes/setup.ts
@@ -48,7 +48,13 @@ function redactSecrets(config: Record<string, unknown>): Record<string, unknown>
   return out;
 }
 
-export async function setupRoutes(app: FastifyInstance, db: Db): Promise<void> {
+export async function setupRoutes(
+  app: FastifyInstance,
+  db: Db,
+  // Called after the set of assignments changes (assign/unassign) so the caller
+  // can refresh anything derived from it — e.g. the device id->lane map.
+  onAssignmentsChanged: () => void = () => {},
+): Promise<void> {
   registerBuiltinDrivers();
   setDeviceLogSink((line) => app.log.info(line));
 
@@ -251,6 +257,7 @@ export async function setupRoutes(app: FastifyInstance, db: Db): Promise<void> {
         enabled: true,
       };
       await db.insert(laneDevices).values(row);
+      onAssignmentsChanged(); // refresh derived state (device->lane map)
       // Don't echo device secrets back (push Digest password, web-UI login, …).
       return reply.code(201).send({
         ...row,
@@ -281,6 +288,7 @@ export async function setupRoutes(app: FastifyInstance, db: Db): Promise<void> {
         .get();
       if (!existing) return reply.code(404).send({ error: "no such device assignment" });
       await db.delete(laneDevices).where(eq(laneDevices.id, req.params.id));
+      onAssignmentsChanged(); // refresh derived state (device->lane map)
       app.log.info(`unassigned device ${req.params.id} (${existing.category}/${existing.driverId}, lane ${existing.lane})`);
       return reply.code(204).send();
     },
diff --git a/apps/server/src/server.ts b/apps/server/src/server.ts
index 24bad88..be38ecc 100644
--- a/apps/server/src/server.ts
+++ b/apps/server/src/server.ts
@@ -5,6 +5,7 @@ import { createDb, type Db } from "@parking/db";
 import { TOKEN_COOKIE, requireJwtSecret } from "./auth.js";
 import { deviceEvents } from "./device-events.js";
 import { EventLog } from "./event-log.js";
+import { LaneMap } from "./lane-map.js";
 import { PrinterMonitor } from "./printer-monitor.js";
 import { buildSigner } from "./signer.js";
 import { authRoutes } from "./routes/auth.js";
@@ -46,9 +47,15 @@ export async function buildServer(opts: BuildOptions = {}): Promise<FastifyInsta
   // Local username/password login → JWT in an HttpOnly cookie + CSRF cookie.
   await authRoutes(app, db);
 
+  // device id -> lane resolver. Built from lane_devices at startup and refreshed
+  // by setupRoutes on assign/unassign, so device events can be stamped with the
+  // lane the device belongs to (events carry the device id, not a lane).
+  const laneMap = new LaneMap(db);
+  laneMap.refresh();
+
   // Device-agnostic setup: the admin selects devices per lane from the driver
   // catalog at first-run. See wiki/concepts/first-run-setup.md.
-  await setupRoutes(app, db);
+  await setupRoutes(app, db, () => laneMap.refresh());
 
   // Inbound device pushes (e.g. Dingtian Input Link URL → button events),
   // guarded by source-IP allowlist + a shared-secret path token, both read from
@@ -72,10 +79,22 @@ export async function buildServer(opts: BuildOptions = {}): Promise<FastifyInsta
   const eventLog = new EventLog(db, buildSigner(app.log));
   await eventRoutes(app, db, eventLog);
   const unsubscribeInput = deviceEvents.onInput((e) => {
+    // Resolve which lane the device belongs to. -1 marks "device fired but isn't
+    // mapped to a lane" (assigned without a lane, or a stale id) — still recorded
+    // faithfully (the chain is append-only) rather than silently dropped or
+    // mis-stamped as lane 0, which is a real lane.
+    const lane = laneMap.laneFor(e.deviceId) ?? -1;
+    if (lane === -1) {
+      app.log.warn(`input from unmapped device ${e.driverId}:${e.deviceId} — logged as lane -1`);
+    }
     eventLog
       .append({
         type: "input_received",
-        lane: 0, // lane mapping is a TODO — device->lane lookup arrives with setup/lane wiring
+        lane,
+        // `source` is an IdentitySource (wiegand/lpr/qr/ticket/manual) — how a
+        // VEHICLE was identified. A raw input has none, so it stays null. The
+        // device provenance lives in `identity` instead.
+        source: null,
         identity: `${e.driverId}:${e.deviceId} input:${e.input}/${e.edge}`,
         occurredAt: e.at,
       })
@@ -83,7 +102,7 @@ export async function buildServer(opts: BuildOptions = {}): Promise<FastifyInsta
   });
   app.addHook("onClose", async () => unsubscribeInput());
 
-  // TODO: entry flow (input event → signed event → print → relay); map device→lane.
+  // TODO: entry flow (input event → signed event → print → relay).
 
   return app;
 }
diff --git a/wiki/concepts/append-only-event-chain.md b/wiki/concepts/append-only-event-chain.md
index 91590f7..833c4ff 100644
--- a/wiki/concepts/append-only-event-chain.md
+++ b/wiki/concepts/append-only-event-chain.md
@@ -2,7 +2,7 @@
 type: concept
 tags: [parking, security, integrity]
 sources: [parking-system-architecture]
-updated: 2026-06-14
+updated: 2026-06-15
 ---
 
 # Append-Only Event Chain
@@ -62,8 +62,18 @@ so old events stay verifiable.
 
 Dingtian **input (button) pushes** → bus → `input_received` events (see [[device-input-flow]],
 [[dingtian-relay]]). These are recorded faithfully as raw inputs, **not** as `vehicle_entry` —
-the richer entry event waits for the entry flow (ticket print + barrier command). Device→lane
-mapping is still a TODO (logged with `lane: 0`).
+the richer entry event waits for the entry flow (ticket print + barrier command).
+
+- **`lane`** is now resolved from the firing device. A `LaneMap` (`apps/server/src/lane-map.ts`)
+  caches `lane_devices.id → lane`, built at startup and refreshed by the setup routes on every
+  assign/unassign. Device events carry the device instance id, not a lane; the handler looks it
+  up. A device with no mapping (assigned without a lane, or a stale id) logs **`lane: -1`** and a
+  warning — never `0`, which is a real lane — and is still recorded (the chain is append-only;
+  nothing is dropped).
+- **`source` stays `null`** for `input_received`, and deliberately so: `source` is an
+  `IdentitySource` (`wiegand | lpr | qr | ticket | manual`) — *how a vehicle was identified* — not
+  a device/IP field. A raw button push has no vehicle identity. The device provenance lives in
+  **`identity`** (e.g. `dingtian:<id> input:1/on`).
 
 ### ⚠️ Limitation: the log captures HOST-ORIGINATED actions only
 
diff --git a/wiki/log.md b/wiki/log.md
index 7ac667a..be19acc 100644
--- a/wiki/log.md
+++ b/wiki/log.md
@@ -288,3 +288,12 @@ guarantee. Recorded in [[dingtian-relay]] (new Hardening section).
 - Verified on hardware (192.168.1.100): harden set login to a chosen pw; device then rejects
   admin/admin (&2&) and accepts the chosen pw (&0&). UDP2 warning surfaced as designed.
 - Updated [[dingtian-relay]].
+
+## [2026-06-15] update | input_received lane resolution + source semantics
+- Wired device→lane resolution: `LaneMap` (`apps/server/src/lane-map.ts`) caches
+  `lane_devices.id → lane`, refreshed by setup routes on assign/unassign. `input_received`
+  events now carry the firing device's lane instead of a hardcoded `lane: 0`. Unmapped device →
+  `lane: -1` + warn (0 is a real lane; never mis-stamp).
+- Documented that `source` stays null for raw inputs by design (it's an IdentitySource, not a
+  device field); device provenance is in `identity`.
+- Updated [[append-only-event-chain]].