diff --git a/src/main/worker/runtime/credential-concurrency-gate.ts b/src/main/worker/runtime/credential-concurrency-gate.ts
new file mode 100644
index 00000000..9740393b
--- /dev/null
+++ b/src/main/worker/runtime/credential-concurrency-gate.ts
@@ -0,0 +1,132 @@
+import { createHash } from "node:crypto";
+
+/**
+ * Per-credential async concurrency gate.
+ *
+ * The gate hands out a bounded number of concurrent slots per
+ * `(provider, apiKey)` pair. When the cap is reached, further
+ * `acquire` calls park until an in-flight caller releases its slot.
+ *
+ * The Boss build seeds a single Fire Pass key shared by every agent.
+ * Without serialization, the worker fans out three or more concurrent
+ * `streamSimple` calls against the personal-tier router and trips
+ * HTTP 429 on every burst. Holding a slot per credential prevents
+ * the burst at the source instead of recovering from it after the
+ * fact, which keeps the runtime aligned with the project's
+ * "let it crash" rule (no retry/backoff fallback layer is added).
+ *
+ * The gate is process-local. Only one orchestrator worker runs at a
+ * time, so a single gate instance correctly serializes every agent
+ * sharing a credential.
+ */
+export type ConcurrencyLimitResolver = (provider: string) => number | null;
+
+export interface CredentialConcurrencyGate {
+  acquire(provider: string, apiKey: string, signal?: AbortSignal): Promise<() => void>;
+}
+
+interface Waiter {
+  notify: () => void;
+  cancel: (err: Error) => void;
+  signal?: AbortSignal;
+  abortListener?: () => void;
+}
+
+interface SlotPool {
+  inFlight: number;
+  readonly limit: number;
+  readonly waiters: Waiter[];
+}
+
+const NOOP_RELEASE = () => undefined;
+
+function poolKey(provider: string, apiKey: string): string {
+  // Hash the apiKey so the Map key cannot echo a raw credential into
+  // heap dumps or future debug output — the gate only needs equality.
+  const digest = createHash("sha1").update(apiKey).digest("hex").slice(0, 16);
+  return `${provider}:${digest}`;
+}
+
+function createAbortError(): Error {
+  const err = new Error("Aborted while waiting for credential concurrency slot.");
+  err.name = "AbortError";
+  return err;
+}
+
+export class InMemoryCredentialConcurrencyGate implements CredentialConcurrencyGate {
+  private readonly pools = new Map<string, SlotPool>();
+  private readonly limitFor: ConcurrencyLimitResolver;
+
+  constructor(limitFor: ConcurrencyLimitResolver) {
+    this.limitFor = limitFor;
+  }
+
+  async acquire(provider: string, apiKey: string, signal?: AbortSignal): Promise<() => void> {
+    const limit = this.limitFor(provider);
+    if (limit === null) return NOOP_RELEASE;
+    if (signal?.aborted) throw createAbortError();
+    const key = poolKey(provider, apiKey);
+    const pool = this.getOrCreatePool(key, limit);
+    if (pool.inFlight < pool.limit) {
+      pool.inFlight += 1;
+      return this.makeReleaser(key);
+    }
+    await this.waitForSlot(pool, signal);
+    pool.inFlight += 1;
+    return this.makeReleaser(key);
+  }
+
+  private getOrCreatePool(key: string, limit: number): SlotPool {
+    const existing = this.pools.get(key);
+    if (existing) return existing;
+    const pool: SlotPool = { inFlight: 0, limit, waiters: [] };
+    this.pools.set(key, pool);
+    return pool;
+  }
+
+  private waitForSlot(pool: SlotPool, signal?: AbortSignal): Promise<void> {
+    return new Promise((resolve, reject) => {
+      const waiter: Waiter = {
+        notify: () => {
+          this.detachAbort(waiter);
+          resolve();
+        },
+        cancel: (err) => {
+          const idx = pool.waiters.indexOf(waiter);
+          if (idx >= 0) pool.waiters.splice(idx, 1);
+          this.detachAbort(waiter);
+          reject(err);
+        },
+        signal,
+      };
+      if (signal) {
+        const onAbort = () => waiter.cancel(createAbortError());
+        waiter.abortListener = onAbort;
+        signal.addEventListener("abort", onAbort, { once: true });
+      }
+      pool.waiters.push(waiter);
+    });
+  }
+
+  private detachAbort(waiter: Waiter): void {
+    if (waiter.abortListener && waiter.signal) {
+      waiter.signal.removeEventListener("abort", waiter.abortListener);
+    }
+  }
+
+  private makeReleaser(key: string): () => void {
+    let released = false;
+    return () => {
+      if (released) return;
+      released = true;
+      const pool = this.pools.get(key);
+      if (!pool) return;
+      pool.inFlight = Math.max(0, pool.inFlight - 1);
+      const next = pool.waiters.shift();
+      if (next) next.notify();
+      if (pool.inFlight === 0 && pool.waiters.length === 0) {
+        this.pools.delete(key);
+      }
+    };
+  }
+}
diff --git a/src/main/worker/runtime/pi-safe-stream.ts b/src/main/worker/runtime/pi-safe-stream.ts
index a353ad4b..98c1430c 100644
--- a/src/main/worker/runtime/pi-safe-stream.ts
+++ b/src/main/worker/runtime/pi-safe-stream.ts
@@ -10,6 +10,11 @@ import {
   type StopReason,
   type Usage,
 } from "@mariozechner/pi-ai";
+import {
+  InMemoryCredentialConcurrencyGate,
+  type CredentialConcurrencyGate,
+} from "./credential-concurrency-gate";
+import { getProviderConcurrencyLimit } from "./provider-rate-limits";
 
 type PiStreamSource = (
   model: Model<Api>,
@@ -67,16 +72,36 @@ function pushStreamError(
   stream.end(message);
 }
 
-export function createSafePiStream(source: PiStreamSource): SafePiStreamSource {
+/**
+ * Build a safe stream wrapper. When `gate` is provided, every call
+ * acquires a slot keyed by `(model.provider, options.apiKey)` before
+ * the underlying source is invoked, and releases the slot once the
+ * stream finishes (success, error, or abort). Calls without an
+ * `apiKey` skip the gate — they target keyless transports such as
+ * local Ollama / LM Studio.
+ */
+export function createSafePiStream(
+  source: PiStreamSource,
+  gate?: CredentialConcurrencyGate,
+): SafePiStreamSource {
   return (model, context, options) => {
     const target = createAssistantMessageEventStream();
+    const apiKey = typeof options?.apiKey === "string" ? options.apiKey : "";
+    const acquireSlot = gate && apiKey
+      ? () => gate.acquire(model.provider, apiKey, options?.signal)
+      : () => Promise.resolve<() => void>(() => undefined);
     void Promise.resolve()
-      .then(() => source(model, context, options))
-      .then(async (sourceStream) => {
-        for await (const event of sourceStream) {
-          target.push(event);
+      .then(acquireSlot)
+      .then(async (release) => {
+        try {
+          const sourceStream = await source(model, context, options);
+          for await (const event of sourceStream) {
+            target.push(event);
+          }
+          target.end();
+        } finally {
+          release();
         }
-        target.end();
       })
       .catch((error) => {
         pushStreamError(target, model, error, options?.signal);
@@ -85,4 +110,8 @@ export function createSafePiStream(source: PiStreamSource): SafePiStreamSource {
   };
 }
 
-export const safeStreamSimple = createSafePiStream(streamSimple);
+const defaultGate: CredentialConcurrencyGate = new InMemoryCredentialConcurrencyGate(
+  getProviderConcurrencyLimit,
+);
+
+export const safeStreamSimple = createSafePiStream(streamSimple, defaultGate);
diff --git a/src/main/worker/runtime/provider-rate-limits.ts b/src/main/worker/runtime/provider-rate-limits.ts
new file mode 100644
index 00000000..4623388c
--- /dev/null
+++ b/src/main/worker/runtime/provider-rate-limits.ts
@@ -0,0 +1,31 @@
+/**
+ * Per-provider concurrency caps applied to outbound model calls.
+ *
+ * Each entry limits the number of in-flight `streamSimple` invocations
+ * that share a single credential (keyed by `provider` + `apiKey`).
+ * Providers absent from the map are treated as uncapped — the gate
+ * short-circuits and the call proceeds immediately.
+ *
+ * `fireworks-firepass` is the load-bearing entry. The Fire Pass router
+ * `accounts/fireworks/routers/kimi-k2p6-turbo` is a personal-tier route:
+ * the subscription documents zero per-token cost but the upstream
+ * router rejects bursts on a single key with HTTP 429. In the Boss
+ * build every agent shares the seeded Fire Pass key, so without a cap
+ * three concurrent agents trip three 429s — the exact failure mode
+ * captured in the overview dashboard. A cap of `1` serializes runs on
+ * the shared key without dropping any work.
+ *
+ * Other providers (`anthropic`, `openai`, `google`, …) advertise
+ * generous tier-based budgets and have no evidence of contention in
+ * the boss or public builds. Leaving them uncapped honours the
+ * project's "let it crash" stance — only providers with a known
+ * upstream constraint are throttled here.
+ */
+export const PROVIDER_CONCURRENCY_LIMITS: Readonly<Record<string, number>> = {
+  "fireworks-firepass": 1,
+};
+
+export function getProviderConcurrencyLimit(provider: string): number | null {
+  const value = PROVIDER_CONCURRENCY_LIMITS[provider];
+  return typeof value === "number" && value > 0 ? value : null;
+}
diff --git a/tests/unit/credential-concurrency-gate.test.ts b/tests/unit/credential-concurrency-gate.test.ts
new file mode 100644
index 00000000..c1fb1b05
--- /dev/null
+++ b/tests/unit/credential-concurrency-gate.test.ts
@@ -0,0 +1,106 @@
+import { describe, expect, it } from "vitest";
+import { InMemoryCredentialConcurrencyGate } from "../../src/main/worker/runtime/credential-concurrency-gate";
+
+function makeGate(limit: number | null) {
+  return new InMemoryCredentialConcurrencyGate(() => limit);
+}
+
+describe("InMemoryCredentialConcurrencyGate", () => {
+  it("returns a no-op release when the provider is uncapped", async () => {
+    const gate = makeGate(null);
+    const release = await gate.acquire("anthropic", "key-x");
+    expect(typeof release).toBe("function");
+    release();
+    release();
+  });
+
+  it("hands out slots up to the limit immediately", async () => {
+    const gate = makeGate(2);
+    const r1 = await gate.acquire("fireworks-firepass", "shared");
+    const r2 = await gate.acquire("fireworks-firepass", "shared");
+    expect(r1).not.toBe(r2);
+    r1();
+    r2();
+  });
+
+  it("queues the third caller until a slot is released", async () => {
+    const gate = makeGate(1);
+    const release = await gate.acquire("fireworks-firepass", "shared");
+    const order: string[] = [];
+
+    const second = (async () => {
+      const r = await gate.acquire("fireworks-firepass", "shared");
+      order.push("second");
+      r();
+    })();
+    const third = (async () => {
+      const r = await gate.acquire("fireworks-firepass", "shared");
+      order.push("third");
+      r();
+    })();
+
+    await new Promise((resolve) => setTimeout(resolve, 10));
+    expect(order).toEqual([]);
+
+    release();
+    await second;
+    expect(order).toEqual(["second"]);
+
+    await third;
+    expect(order).toEqual(["second", "third"]);
+  });
+
+  it("scopes pools by (provider, apiKey) so different keys do not block each other", async () => {
+    const gate = makeGate(1);
+    const r1 = await gate.acquire("fireworks-firepass", "key-a");
+    // Different apiKey -> new pool, no waiting.
+    const r2 = await gate.acquire("fireworks-firepass", "key-b");
+    expect(typeof r1).toBe("function");
+    expect(typeof r2).toBe("function");
+    r1();
+    r2();
+  });
+
+  it("releases the pool when no callers remain", async () => {
+    const gate = makeGate(1);
+    const release = await gate.acquire("fireworks-firepass", "shared");
+    release();
+    // Re-acquire should not be queued.
+    const next = await gate.acquire("fireworks-firepass", "shared");
+    next();
+  });
+
+  it("rejects when the abort signal fires while waiting", async () => {
+    const gate = makeGate(1);
+    const held = await gate.acquire("fireworks-firepass", "shared");
+
+    const controller = new AbortController();
+    const pending = gate.acquire("fireworks-firepass", "shared", controller.signal);
+    controller.abort();
+
+    await expect(pending).rejects.toMatchObject({ name: "AbortError" });
+
+    // Slot must remain available after the aborted waiter is removed.
+    held();
+    const next = await gate.acquire("fireworks-firepass", "shared");
+    next();
+  });
+
+  it("rejects immediately when the abort signal is already aborted", async () => {
+    const gate = makeGate(1);
+    const controller = new AbortController();
+    controller.abort();
+    await expect(
+      gate.acquire("fireworks-firepass", "shared", controller.signal),
+    ).rejects.toMatchObject({ name: "AbortError" });
+  });
+
+  it("treats double-release as a no-op", async () => {
+    const gate = makeGate(1);
+    const release = await gate.acquire("fireworks-firepass", "shared");
+    release();
+    release();
+    const next = await gate.acquire("fireworks-firepass", "shared");
+    next();
+  });
+});
diff --git a/tests/unit/pi-safe-stream.test.ts b/tests/unit/pi-safe-stream.test.ts
index 5549fe65..a689cc78 100644
--- a/tests/unit/pi-safe-stream.test.ts
+++ b/tests/unit/pi-safe-stream.test.ts
@@ -7,6 +7,7 @@ import {
 } from "@mariozechner/pi-ai";
 import { describe, expect, it } from "vitest";
 import { createSafePiStream } from "../../src/main/worker/runtime/pi-safe-stream";
+import { InMemoryCredentialConcurrencyGate } from "../../src/main/worker/runtime/credential-concurrency-gate";
 
 function createModel(): Model<"openai-responses"> {
   return {
@@ -67,6 +68,102 @@ describe("pi safe stream", () => {
     await expect(stream.result()).resolves.toMatchObject({ stopReason: "stop" });
   });
 
+  it("serializes calls that share a gated credential", async () => {
+    const gate = new InMemoryCredentialConcurrencyGate(() => 1);
+    let activeCalls = 0;
+    let peakActive = 0;
+
+    const safeStream = createSafePiStream((_model, _context) => {
+      activeCalls += 1;
+      peakActive = Math.max(peakActive, activeCalls);
+      const stream = createAssistantMessageEventStream();
+      setTimeout(() => {
+        const message = createAssistantMessage();
+        stream.push({ type: "done", reason: "stop", message });
+        stream.end(message);
+        activeCalls -= 1;
+      }, 5);
+      return stream;
+    }, gate);
+
+    const drain = async (stream: ReturnType<typeof safeStream>) => {
+      for await (const _event of stream) {
+        // drain
+      }
+      await stream.result();
+    };
+
+    const model = createModel();
+    const a = safeStream(model, emptyContext, { apiKey: "shared" });
+    const b = safeStream(model, emptyContext, { apiKey: "shared" });
+    const c = safeStream(model, emptyContext, { apiKey: "shared" });
+
+    await Promise.all([drain(a), drain(b), drain(c)]);
+    expect(peakActive).toBe(1);
+  });
+
+  it("does not gate calls without an apiKey", async () => {
+    const gate = new InMemoryCredentialConcurrencyGate(() => 1);
+    let activeCalls = 0;
+    let peakActive = 0;
+
+    const safeStream = createSafePiStream((_model, _context) => {
+      activeCalls += 1;
+      peakActive = Math.max(peakActive, activeCalls);
+      const stream = createAssistantMessageEventStream();
+      setTimeout(() => {
+        const message = createAssistantMessage();
+        stream.push({ type: "done", reason: "stop", message });
+        stream.end(message);
+        activeCalls -= 1;
+      }, 5);
+      return stream;
+    }, gate);
+
+    const drain = async (stream: ReturnType<typeof safeStream>) => {
+      for await (const _event of stream) {
+        // drain
+      }
+      await stream.result();
+    };
+
+    const model = createModel();
+    await Promise.all([
+      drain(safeStream(model, emptyContext)),
+      drain(safeStream(model, emptyContext)),
+    ]);
+    expect(peakActive).toBe(2);
+  });
+
+  it("releases the slot when the upstream stream throws", async () => {
+    const gate = new InMemoryCredentialConcurrencyGate(() => 1);
+    let attempt = 0;
+
+    const safeStream = createSafePiStream(() => {
+      attempt += 1;
+      if (attempt === 1) throw new Error("first call boom");
+      const stream = createAssistantMessageEventStream();
+      queueMicrotask(() => {
+        const message = createAssistantMessage();
+        stream.push({ type: "done", reason: "stop", message });
+        stream.end(message);
+      });
+      return stream;
+    }, gate);
+
+    const failing = safeStream(createModel(), emptyContext, { apiKey: "shared" });
+    for await (const _event of failing) {
+      // drain
+    }
+    await failing.result();
+
+    const succeeding = safeStream(createModel(), emptyContext, { apiKey: "shared" });
+    for await (const _event of succeeding) {
+      // drain
+    }
+    await expect(succeeding.result()).resolves.toMatchObject({ stopReason: "stop" });
+  });
+
   it("turns rejected stream setup into an error event", async () => {
     const safeStream = createSafePiStream(async () => {
       throw new Error("stream setup failed");
diff --git a/tests/unit/provider-rate-limits.test.ts b/tests/unit/provider-rate-limits.test.ts
new file mode 100644
index 00000000..36608a57
--- /dev/null
+++ b/tests/unit/provider-rate-limits.test.ts
@@ -0,0 +1,19 @@
+import { describe, expect, it } from "vitest";
+import {
+  PROVIDER_CONCURRENCY_LIMITS,
+  getProviderConcurrencyLimit,
+} from "../../src/main/worker/runtime/provider-rate-limits";
+
+describe("provider rate limits", () => {
+  it("caps fireworks-firepass at one concurrent call", () => {
+    expect(PROVIDER_CONCURRENCY_LIMITS["fireworks-firepass"]).toBe(1);
+    expect(getProviderConcurrencyLimit("fireworks-firepass")).toBe(1);
+  });
+
+  it("returns null for providers without an explicit cap", () => {
+    expect(getProviderConcurrencyLimit("anthropic")).toBeNull();
+    expect(getProviderConcurrencyLimit("openai")).toBeNull();
+    expect(getProviderConcurrencyLimit("ollama")).toBeNull();
+    expect(getProviderConcurrencyLimit("unknown-provider")).toBeNull();
+  });
+});