diff --git a/src/lib/inflight-tracker.ts b/src/lib/inflight-tracker.ts
new file mode 100644
index 0000000..ad5dbba
--- /dev/null
+++ b/src/lib/inflight-tracker.ts
@@ -0,0 +1,58 @@
+export interface InflightRequest {
+  id?: string;
+  model: string;
+  req_path?: string;
+  method?: string;
+  timestamp?: string;
+  elapsed_ms?: number;
+}
+
+export interface ModelState {
+  id: string;
+  state: string;
+}
+
+export type FeedEvent =
+  | { type: "inflight"; operation: "snapshot" | "add" | "remove"; requests: InflightRequest[] }
+  | { type: "modelStatus"; models: ModelState[] };
+
+export type ModelRuntimeState = "stopped" | "loading" | "ready";
+
+export class InflightTracker {
+  private counts = new Map<string, number>();
+  private states = new Map<string, ModelRuntimeState>();
+
+  apply(event: FeedEvent): void {
+    if (event.type === "inflight") {
+      if (event.operation === "snapshot") {
+        const counts = new Map<string, number>();
+        for (const r of event.requests) counts.set(r.model, (counts.get(r.model) ?? 0) + 1);
+        this.counts = counts;
+      } else if (event.operation === "add") {
+        for (const r of event.requests) this.counts.set(r.model, (this.counts.get(r.model) ?? 0) + 1);
+      } else if (event.operation === "remove") {
+        for (const r of event.requests) {
+          const c = this.counts.get(r.model) ?? 0;
+          if (c <= 1) this.counts.delete(r.model);
+          else this.counts.set(r.model, c - 1);
+        }
+      }
+    } else if (event.type === "modelStatus") {
+      for (const m of event.models) this.states.set(m.id, normalizeState(m.state));
+    }
+  }
+
+  count(modelId: string): number {
+    return this.counts.get(modelId) ?? 0;
+  }
+
+  state(modelId: string): ModelRuntimeState | undefined {
+    return this.states.get(modelId);
+  }
+}
+
+function normalizeState(state: string): ModelRuntimeState {
+  if (state === "ready") return "ready";
+  if (state === "loading") return "loading";
+  return "stopped";
+}
diff --git a/src/lib/sse.ts b/src/lib/sse.ts
new file mode 100644
index 0000000..01fa21b
--- /dev/null
+++ b/src/lib/sse.ts
@@ -0,0 +1,29 @@
+export interface SseMessage {
+  event?: string;
+  data: string;
+}
+
+export function parseSse(chunk: string): { messages: SseMessage[]; rest: string } {
+  const messages: SseMessage[] = [];
+  let rest = chunk;
+  while (true) {
+    const idx = rest.indexOf("\n\n");
+    if (idx === -1) break;
+    const block = rest.slice(0, idx);
+    rest = rest.slice(idx + 2);
+    const message = toMessage(block);
+    if (message && message.data.length > 0) messages.push(message);
+  }
+  return { messages, rest };
+}
+
+function toMessage(block: string): SseMessage | null {
+  let event: string | undefined;
+  const dataLines: string[] = [];
+  for (const line of block.split("\n")) {
+    if (line.startsWith("event:")) event = line.slice(6).trim();
+    else if (line.startsWith("data:")) dataLines.push(line.slice(5).trimStart());
+  }
+  if (dataLines.length === 0) return null;
+  return { event, data: dataLines.join("\n") };
+}
diff --git a/tests/inflight-tracker.test.ts b/tests/inflight-tracker.test.ts
new file mode 100644
index 0000000..0396cbe
--- /dev/null
+++ b/tests/inflight-tracker.test.ts
@@ -0,0 +1,50 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { InflightTracker, type FeedEvent } from "../src/lib/inflight-tracker";
+
+test("snapshot rebuilds counts for all in-flight requests", () => {
+  const tracker = new InflightTracker();
+  tracker.apply({
+    type: "inflight",
+    operation: "snapshot",
+    requests: [
+      { model: "A", id: "1" },
+      { model: "A", id: "2" },
+      { model: "B", id: "3" },
+    ],
+  });
+  assert.equal(tracker.count("A"), 2);
+  assert.equal(tracker.count("B"), 1);
+  assert.equal(tracker.count("C"), 0);
+});
+
+test("add and remove adjust per-model counts", () => {
+  const tracker = new InflightTracker();
+  tracker.apply({ type: "inflight", operation: "add", requests: [{ model: "A", id: "1" }] });
+  tracker.apply({ type: "inflight", operation: "add", requests: [{ model: "A", id: "2" }] });
+  assert.equal(tracker.count("A"), 2);
+  tracker.apply({ type: "inflight", operation: "remove", requests: [{ model: "A", id: "1" }] });
+  assert.equal(tracker.count("A"), 1);
+  tracker.apply({ type: "inflight", operation: "remove", requests: [{ model: "A", id: "2" }] });
+  assert.equal(tracker.count("A"), 0);
+  tracker.apply({ type: "inflight", operation: "remove", requests: [{ model: "A", id: "9" }] });
+  assert.equal(tracker.count("A"), 0);
+});
+
+test("modelStatus normalizes states", () => {
+  const tracker = new InflightTracker();
+  tracker.apply({
+    type: "modelStatus",
+    models: [
+      { id: "A", state: "ready" },
+      { id: "B", state: "loading" },
+      { id: "C", state: "stopped" },
+      { id: "D", state: "weird" },
+    ],
+  });
+  assert.equal(tracker.state("A"), "ready");
+  assert.equal(tracker.state("B"), "loading");
+  assert.equal(tracker.state("C"), "stopped");
+  assert.equal(tracker.state("D"), "stopped");
+  assert.equal(tracker.state("missing"), undefined);
+});
diff --git a/tests/sse.test.ts b/tests/sse.test.ts
new file mode 100644
index 0000000..4c71b43
--- /dev/null
+++ b/tests/sse.test.ts
@@ -0,0 +1,24 @@
+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { parseSse } from "../src/lib/sse";
+
+test("parseSse extracts event + data blocks separated by blank lines", () => {
+  const { messages, rest } = parseSse('event:message\ndata:{"a":1}\n\nevent:message\ndata:hello\n\n');
+  assert.equal(rest, "");
+  assert.equal(messages.length, 2);
+  assert.equal(messages[0].event, "message");
+  assert.equal(messages[0].data, '{"a":1}');
+  assert.equal(messages[1].data, "hello");
+});
+
+test("parseSse keeps a trailing partial event in rest", () => {
+  const { messages, rest } = parseSse("event:message\ndata:par");
+  assert.equal(messages.length, 0);
+  assert.equal(rest, "event:message\ndata:par");
+});
+
+test("parseSse joins multi-line data fields with newline", () => {
+  const { messages } = parseSse("data:line1\ndata:line2\n\n");
+  assert.equal(messages.length, 1);
+  assert.equal(messages[0].data, "line1\nline2");
+});