diff --git a/packages/server/src/server/agent/agent-prompt.test.ts b/packages/server/src/server/agent/agent-prompt.test.ts
index 89b175d13..864813a14 100644
--- a/packages/server/src/server/agent/agent-prompt.test.ts
+++ b/packages/server/src/server/agent/agent-prompt.test.ts
@@ -1,5 +1,9 @@
 import { expect, it, test, vi } from "vitest";
 import pino, { type Logger } from "pino";
+import { randomUUID } from "node:crypto";
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
 
 import { createTestLogger } from "../../test-utils/test-logger.js";
 import { AgentManager } from "./agent-manager.js";
@@ -8,8 +12,15 @@ import {
   formatSystemNotificationPrompt,
   isSystemInjectedEnvelope,
   setupFinishNotification,
+  waitForAgentRunStartWithTimeout,
 } from "./agent-prompt.js";
 import type { AgentManagerEvent, ManagedAgent } from "./agent-manager.js";
+import type {
+  AgentClient,
+  AgentRunResult,
+  AgentSession,
+  AgentStreamEvent,
+} from "./agent-sdk-types.js";
 
 interface CapturedLogger {
   logger: Logger;
@@ -520,3 +531,234 @@ it("does not notify archived callers", async () => {
   expect(streamAgentSpy).not.toHaveBeenCalled();
   expect(replaceAgentRunSpy).not.toHaveBeenCalled();
 });
+
+// Deliberately independent literals rather than the production constants these tests
+// guard: deriving the boundaries from AGENT_RUN_START_TIMEOUT_MS would keep the tests
+// green if that constant were shortened back under a provider's startup budget.
+const EXPECTED_RUN_START_BUDGET_MS = 60_000;
+// The slowest provider startup budget the run-start wait has to sit outside of today
+// (OpenCode's OPENCODE_SERVER_STARTUP_TIMEOUT_MS).
+const SLOWEST_PROVIDER_STARTUP_BUDGET_MS = 30_000;
+
+const RUN_START_TEST_CAPABILITIES = {
+  supportsStreaming: false,
+  supportsSessionPersistence: false,
+  supportsSessionListing: true,
+  supportsDynamicModes: false,
+  supportsMcpServers: false,
+  supportsReasoningStream: false,
+  supportsToolInvocations: false,
+} as const;
+
+/**
+ * Provider session whose turn start is held open for a configurable span, so the real
+ * AgentManager run-state transition (pendingRun.started -> lifecycle "running" ->
+ * agent_state) is what the run-start wait observes. `startDelayMs: null` never starts.
+ */
+class SlowStartAgentSession implements AgentSession {
+  readonly provider = "codex" as const;
+  readonly capabilities = RUN_START_TEST_CAPABILITIES;
+  readonly id = randomUUID();
+  private readonly subscribers = new Set<(event: AgentStreamEvent) => void>();
+  private releaseStartTurn!: () => void;
+  private readonly released = new Promise<void>((resolve) => {
+    this.releaseStartTurn = resolve;
+  });
+
+  constructor(private readonly startDelayMs: number | null) {}
+
+  async run(): Promise<AgentRunResult> {
+    return { sessionId: this.id, finalText: "", timeline: [] };
+  }
+
+  /** Teardown hook so a never-starting turn cannot wedge the suite. */
+  release(): void {
+    this.releaseStartTurn();
+  }
+
+  async startTurn(): Promise<{ turnId: string }> {
+    await new Promise<void>((resolve) => {
+      if (this.startDelayMs !== null) {
+        setTimeout(resolve, this.startDelayMs);
+      }
+      void this.released.then(resolve);
+    });
+    const turnId = "turn-1";
+    setTimeout(() => {
+      this.pushEvent({ type: "turn_started", provider: this.provider, turnId });
+      this.pushEvent({ type: "turn_completed", provider: this.provider, turnId });
+    }, 0);
+    return { turnId };
+  }
+
+  subscribe(callback: (event: AgentStreamEvent) => void): () => void {
+    this.subscribers.add(callback);
+    return () => {
+      this.subscribers.delete(callback);
+    };
+  }
+
+  pushEvent(event: AgentStreamEvent): void {
+    for (const callback of this.subscribers) {
+      callback(event);
+    }
+  }
+
+  async *streamHistory(): AsyncGenerator<AgentStreamEvent> {}
+
+  async getRuntimeInfo() {
+    return { provider: this.provider, sessionId: this.id, model: null, modeId: null };
+  }
+
+  async getAvailableModes() {
+    return [];
+  }
+
+  async getCurrentMode() {
+    return null;
+  }
+
+  async setMode(): Promise<void> {}
+
+  getPendingPermissions() {
+    return [];
+  }
+
+  async respondToPermission(): Promise<void> {}
+
+  describePersistence() {
+    return { provider: this.provider, sessionId: this.id };
+  }
+
+  async interrupt(): Promise<void> {}
+
+  async close(): Promise<void> {}
+}
+
+class SlowStartAgentClient implements AgentClient {
+  readonly provider = "codex" as const;
+  readonly capabilities = RUN_START_TEST_CAPABILITIES;
+  readonly sessions: SlowStartAgentSession[] = [];
+
+  constructor(private readonly startDelayMs: number | null) {}
+
+  async isAvailable(): Promise<boolean> {
+    return true;
+  }
+
+  async createSession(): Promise<AgentSession> {
+    const session = new SlowStartAgentSession(this.startDelayMs);
+    this.sessions.push(session);
+    return session;
+  }
+
+  async fetchCatalog() {
+    return { models: [], modes: [] };
+  }
+
+  async resumeSession(): Promise<AgentSession> {
+    return await this.createSession();
+  }
+}
+
+/**
+ * Real AgentManager driving a real agent, so the run-start wait exercises the production
+ * run-state and agent_state subscription path rather than a replaced method.
+ */
+async function createRunStartScenario(startDelayMs: number | null): Promise<{
+  agentManager: AgentManager;
+  agentId: string;
+  startRun: () => Promise<void>;
+  cleanup: () => Promise<void>;
+}> {
+  const workdir = mkdtempSync(join(tmpdir(), "agent-run-start-budget-"));
+  const client = new SlowStartAgentClient(startDelayMs);
+  const agentManager = new AgentManager({
+    clients: { codex: client },
+    logger: createTestLogger(),
+  });
+  const snapshot = await agentManager.createAgent({ provider: "codex", cwd: workdir }, undefined, {
+    workspaceId: undefined,
+  });
+
+  let drained: Promise<void> = Promise.resolve();
+  return {
+    agentManager,
+    agentId: snapshot.id,
+    // streamAgent registers the pending run synchronously, so the wait always observes it.
+    startRun: async () => {
+      const run = agentManager.streamAgent(snapshot.id, "start the run");
+      drained = (async () => {
+        for await (const _event of run) {
+          // Drain whatever the turn produces.
+        }
+      })().catch(() => undefined);
+    },
+    cleanup: async () => {
+      // Release any turn still held open, then close. The drain is deliberately not
+      // awaited: depending on how far the turn got, the stream ends either from the
+      // release or from the close, and teardown must not depend on which.
+      for (const session of client.sessions) {
+        session.release();
+      }
+      await agentManager.closeAgent(snapshot.id).catch(() => undefined);
+      void drained;
+      rmSync(workdir, { recursive: true, force: true });
+    },
+  };
+}
+
+test("waiting for a run start outlasts the slowest provider startup budget", async () => {
+  // A provider is still allowed to be starting here, so the outer wait must not abort it.
+  const scenario = await createRunStartScenario(SLOWEST_PROVIDER_STARTUP_BUDGET_MS + 5_000);
+  vi.useFakeTimers();
+
+  try {
+    await scenario.startRun();
+    const wait = waitForAgentRunStartWithTimeout(scenario.agentManager, scenario.agentId);
+    let settled = false;
+    const markSettled = () => {
+      settled = true;
+    };
+    void wait.then(markSettled, markSettled);
+
+    await vi.advanceTimersByTimeAsync(SLOWEST_PROVIDER_STARTUP_BUDGET_MS);
+    expect(settled).toBe(false);
+    expect(scenario.agentManager.getAgent(scenario.agentId)?.lifecycle).not.toBe("running");
+
+    await vi.advanceTimersByTimeAsync(5_000);
+    await expect(wait).resolves.toBeUndefined();
+    expect(scenario.agentManager.getAgent(scenario.agentId)?.lifecycle).toBe("running");
+  } finally {
+    vi.useRealTimers();
+    await scenario.cleanup();
+  }
+});
+
+test("waiting for a run start still gives up at the run start budget", async () => {
+  const scenario = await createRunStartScenario(null);
+  vi.useFakeTimers();
+
+  try {
+    await scenario.startRun();
+    const wait = waitForAgentRunStartWithTimeout(scenario.agentManager, scenario.agentId);
+    const rejection = expect(wait).rejects.toThrow(
+      "codex run did not start within 60 seconds (phase: run start)",
+    );
+    let settled = false;
+    const markSettled = () => {
+      settled = true;
+    };
+    void wait.then(markSettled, markSettled);
+
+    await vi.advanceTimersByTimeAsync(EXPECTED_RUN_START_BUDGET_MS - 1);
+    expect(settled).toBe(false);
+
+    await vi.advanceTimersByTimeAsync(1);
+    await rejection;
+    expect(settled).toBe(true);
+  } finally {
+    vi.useRealTimers();
+    await scenario.cleanup();
+  }
+});
diff --git a/packages/server/src/server/agent/agent-prompt.ts b/packages/server/src/server/agent/agent-prompt.ts
index 07c7b4f57..93f2adac5 100644
--- a/packages/server/src/server/agent/agent-prompt.ts
+++ b/packages/server/src/server/agent/agent-prompt.ts
@@ -212,14 +212,35 @@ export interface StartCreatedAgentInitialPromptParams {
   logger: Logger;
 }
 
-const AGENT_RUN_START_TIMEOUT_MS = 15_000;
+/**
+ * Outer bound on a run reaching "started" after dispatch.
+ *
+ * This wraps provider startup, so it MUST stay larger than the slowest provider's own
+ * startup budget — otherwise it aborts a start the provider was still allowed to be
+ * working on, and the provider's budget can never apply. OpenCode is the slowest today:
+ * up to 30s for the server to boot (OPENCODE_SERVER_STARTUP_TIMEOUT_MS) and then a
+ * session.create on the same budget, so this is deliberately set well above 30s.
+ *
+ * Not derived from the provider constant on purpose: this module is provider-agnostic
+ * and must not depend on a specific provider's internals.
+ */
+const AGENT_RUN_START_TIMEOUT_MS = 60_000;
 
 export async function waitForAgentRunStartWithTimeout(
   agentManager: AgentManager,
   agentId: string,
 ): Promise<void> {
+  const provider = agentManager.getAgent(agentId)?.provider ?? "provider";
   const startAbort = new AbortController();
-  const startTimeout = setTimeout(() => startAbort.abort("timeout"), AGENT_RUN_START_TIMEOUT_MS);
+  const startTimeout = setTimeout(
+    () =>
+      startAbort.abort(
+        new Error(
+          `${provider} run did not start within ${AGENT_RUN_START_TIMEOUT_MS / 1000} seconds (phase: run start)`,
+        ),
+      ),
+    AGENT_RUN_START_TIMEOUT_MS,
+  );
 
   try {
     await agentManager.waitForAgentRunStart(agentId, { signal: startAbort.signal });
diff --git a/packages/server/src/server/agent/providers/opencode-agent.test.ts b/packages/server/src/server/agent/providers/opencode-agent.test.ts
index 807f9151c..8e4cdd9f6 100644
--- a/packages/server/src/server/agent/providers/opencode-agent.test.ts
+++ b/packages/server/src/server/agent/providers/opencode-agent.test.ts
@@ -343,6 +343,81 @@ describe("OpenCodeAgentClient adapter smoke tests", () => {
     rmSync(cwd, { recursive: true, force: true });
   }, 60_000);
 
+  test("creates a session when session.create needs more than ten seconds", async () => {
+    vi.useFakeTimers();
+    const cwd = tmpCwd();
+    const runtime = new TestOpenCodeHarness();
+    const openCode = new TestOpenCodeClient();
+    const slowCreate = createTestDeferred<void>();
+    openCode.sessionCreateImplementation = async () => {
+      await slowCreate.promise;
+      return { data: { id: "session-1" } };
+    };
+    runtime.enqueueClient(openCode);
+    const client = new OpenCodeAgentClient(logger, undefined, {
+      serverManager: runtime,
+      createClient: runtime.createClient,
+    });
+
+    try {
+      const creation = client.createSession(buildConfig(cwd));
+      let settled = false;
+      const markSettled = () => {
+        settled = true;
+      };
+      void creation.then(markSettled, markSettled);
+
+      // Under CPU contention a per-directory bootstrap has been measured well past ten
+      // seconds, which the previous budget failed outright.
+      await vi.advanceTimersByTimeAsync(20_000);
+      expect(settled).toBe(false);
+
+      slowCreate.resolve();
+      const session = await creation;
+      expect(session.provider).toBe("opencode");
+      expect(openCode.calls.sessionCreate).toHaveLength(1);
+      await session.close();
+    } finally {
+      vi.useRealTimers();
+      slowCreate.resolve();
+      rmSync(cwd, { recursive: true, force: true });
+    }
+  });
+
+  test("bounds session.create at the server startup budget", async () => {
+    vi.useFakeTimers();
+    const cwd = tmpCwd();
+    const runtime = new TestOpenCodeHarness();
+    const openCode = new TestOpenCodeClient();
+    openCode.sessionCreateImplementation = () => new Promise<never>(() => undefined);
+    runtime.enqueueClient(openCode);
+    const client = new OpenCodeAgentClient(logger, undefined, {
+      serverManager: runtime,
+      createClient: runtime.createClient,
+    });
+
+    try {
+      const creation = client.createSession(buildConfig(cwd));
+      const rejection = expect(creation).rejects.toThrow("OpenCode session.create timed out");
+      let settled = false;
+      const markSettled = () => {
+        settled = true;
+      };
+      void creation.then(markSettled, markSettled);
+
+      await vi.advanceTimersByTimeAsync(EXPECTED_STARTUP_BUDGET_MS - 1);
+      expect(settled).toBe(false);
+
+      await vi.advanceTimersByTimeAsync(1);
+      await rejection;
+      expect(settled).toBe(true);
+      expect(runtime.acquisitions.at(-1)?.releaseCount).toBe(1);
+    } finally {
+      vi.useRealTimers();
+      rmSync(cwd, { recursive: true, force: true });
+    }
+  });
+
   test("archives and unarchives the durable native session through client hooks", async () => {
     const cwd = tmpCwd();
     const runtime = new TestOpenCodeHarness();
diff --git a/packages/server/src/server/agent/providers/opencode-agent.ts b/packages/server/src/server/agent/providers/opencode-agent.ts
index c17afc355..e48266a8b 100644
--- a/packages/server/src/server/agent/providers/opencode-agent.ts
+++ b/packages/server/src/server/agent/providers/opencode-agent.ts
@@ -1396,10 +1396,15 @@ export class OpenCodeAgentClient implements AgentClient {
     });
 
     try {
+      // Creating the first session for a directory is part of OpenCode coming up, so it
+      // shares the server startup budget instead of a shorter one that fails agent
+      // creation on contended cold starts.
       const response = await withTimeout(
         client.session.create({ directory: openCodeConfig.cwd }),
-        10_000,
-        "OpenCode session.create timed out after 10s",
+        OPENCODE_SERVER_STARTUP_TIMEOUT_MS,
+        `OpenCode session.create timed out after ${Math.round(
+          OPENCODE_SERVER_STARTUP_TIMEOUT_MS / 1000,
+        )}s`,
       );
 
       if (response.error) {
diff --git a/packages/server/src/server/agent/providers/opencode/test-utils/test-opencode-harness.ts b/packages/server/src/server/agent/providers/opencode/test-utils/test-opencode-harness.ts
index 2f1a29d82..444a5a07b 100644
--- a/packages/server/src/server/agent/providers/opencode/test-utils/test-opencode-harness.ts
+++ b/packages/server/src/server/agent/providers/opencode/test-utils/test-opencode-harness.ts
@@ -145,6 +145,7 @@ export class TestOpenCodeClient {
   sessionCommandEvents: unknown[] = [idleEvent()];
   sessionCommandResponse: OpenCodeResponse = {};
   sessionCreateResponse: OpenCodeResponse = { data: { id: "session-1" } };
+  sessionCreateImplementation: ((parameters: unknown) => Promise<OpenCodeResponse>) | null = null;
   sessionDeleteResponse: OpenCodeResponse = {};
   sessionChildrenResponses: OpenCodeResponse[] = [];
   sessionChildrenImplementation:
@@ -294,6 +295,9 @@ export class TestOpenCodeClient {
         },
         create: async (parameters: unknown) => {
           this.calls.sessionCreate.push(parameters);
+          if (this.sessionCreateImplementation) {
+            return await this.sessionCreateImplementation(parameters);
+          }
           return this.sessionCreateResponse;
         },
         delete: async (parameters: unknown) => {