@@ -6,6 +6,7 @@ const {
   create,
   list,
   connect,
+  pause,
   nextItems,
   getInfo,
   writeFile,
@@ -22,6 +23,7 @@ const {
   create: vi.fn(),
   list: vi.fn(),
   connect: vi.fn(),
+  pause: vi.fn(),
   nextItems: vi.fn(),
   getInfo: vi.fn(),
   writeFile: vi.fn(),
@@ -36,22 +38,27 @@ const {
   NotFoundError: class NotFoundError extends Error {},
 }))
 vi.mock('@e2b/code-interpreter', () => ({
-  Sandbox: { create, list, connect, getInfo },
+  Sandbox: { create, list, connect, pause, getInfo },
   NotFoundError,
 }))
 vi.mock('@/lib/execution/remote-sandbox/session-lock', () => ({
   withSandboxSessionLock: sessionLock,
 }))
 
-import { e2bProvider, stopE2BSessionProcess } from '@/lib/execution/remote-sandbox/e2b'
+import {
+  E2B_MAX_SANDBOX_LIFETIME_MS,
+  e2bProvider,
+  stopE2BSessionProcess,
+} from '@/lib/execution/remote-sandbox/e2b'
 import { observeSandboxExecution } from '@/lib/execution/remote-sandbox/execution-observer'
 
 setEnv({ E2B_API_KEY: 'test', MOTHERSHIP_E2B_TEMPLATE_ID: 'mothership-template' })
 
 function candidate(sandboxId: string, time: number) {
   return {
     sandboxId,
-    startedAt: new Date(time),
+    state: 'running',
+    startedAt: new Date(Date.now() - 3_600_000 + time),
     endAt: new Date(Date.now() + 3_600_000),
     metadata: { simSessionKey: 'chat', simSessionOwnership: 'tracked-v1' },
   }
@@ -681,3 +688,117 @@ describe('E2B session lease', () => {
     expect(plane.requests).toBe(3)
   })
 })
+
+describe('E2B continuous-runtime cap', () => {
+  const CAP_MS = E2B_MAX_SANDBOX_LIFETIME_MS
+  const LEASE_MS = 21 * 60_000
+
+  /** Models E2B: every timeout is clamped to the cap, and resuming a paused sandbox restarts it. */
+  function cappedPlane(runningForMs: number) {
+    const plane = { startedAtMs: Date.now() - runningForMs, endAtMs: 0, paused: false }
+    const clampedEnd = (timeoutMs: number) =>
+      Math.min(Date.now() + timeoutMs, plane.startedAtMs + CAP_MS)
+    plane.endAtMs = clampedEnd(5 * 60_000)
+    list.mockReturnValue({ nextItems, hasNext: false })
+    nextItems.mockImplementation(async () => [
+      {
+        ...candidate('retained', 0),
+        state: plane.paused ? 'paused' : 'running',
+        startedAt: new Date(plane.startedAtMs),
+        endAt: new Date(plane.endAtMs),
+      },
+    ])
+    pause.mockImplementation(async () => {
+      plane.paused = true
+      return true
+    })
+    const sandbox = {
+      sandboxId: 'retained',
+      getInfo: async () => ({ endAt: new Date(plane.endAtMs) }),
+      setTimeout: async (timeoutMs: number) => {
+        plane.endAtMs = clampedEnd(timeoutMs)
+      },
+      commands: {
+        run: async (_command: string, options: { background?: boolean }) => {
+          if (options.background === false) {
+            return { stdout: '{"settled": true}', stderr: '', exitCode: 0 }
+          }
+          throw Object.assign(new Error('Sandbox timeout: end of life'), { name: 'TimeoutError' })
+        },
+      },
+    }
+    connect.mockImplementation(async (_id: string, options: { timeoutMs: number }) => {
+      if (plane.paused) {
+        plane.paused = false
+        plane.startedAtMs = Date.now()
+      }
+      plane.endAtMs = clampedEnd(options.timeoutMs)
+      return sandbox
+    })
+    return plane
+  }
+
+  it('never records a reused lease past the cap when the runtime cannot be reset', async () => {
+    const plane = cappedPlane(CAP_MS - 10 * 60_000)
+    pause.mockRejectedValueOnce(new Error('pause unavailable'))
+    const sandbox = await e2bProvider.findSessionSandbox?.('chat', { lifetimeMs: LEASE_MS })
+    const now = Date.now()
+    expect(plane.endAtMs).toBeLessThan(now + LEASE_MS)
+    expect(sandbox?.outlives?.(LEASE_MS, now)).toBe(false)
+    expect(sandbox?.outlives?.(plane.endAtMs - now - 1000, now)).toBe(true)
+    await sandbox?.extendLifetime?.(LEASE_MS)
+    expect(sandbox?.outlives?.(LEASE_MS, Date.now())).toBe(false)
+  })
+
+  it('pauses and resumes a workbench whose lease would outrun the cap', async () => {
+    const plane = cappedPlane(CAP_MS - 10 * 60_000)
+    const requestedAtMs = Date.now()
+    const sandbox = await e2bProvider.findSessionSandbox?.('chat', { lifetimeMs: LEASE_MS })
+    expect(plane.startedAtMs).toBeGreaterThanOrEqual(requestedAtMs)
+    expect(plane.endAtMs).toBeGreaterThanOrEqual(requestedAtMs + LEASE_MS)
+    expect(sandbox?.outlives?.(LEASE_MS, requestedAtMs)).toBe(true)
+  })
+
+  it('reports reaching the cap as the provider limit, not a user timeout', async () => {
+    cappedPlane(CAP_MS - 30_000)
+    pause.mockRejectedValueOnce(new Error('pause unavailable'))
+    const sandbox = await e2bProvider.findSessionSandbox?.('chat', { lifetimeMs: LEASE_MS })
+    const result = await sandbox?.runCommand('long job', { timeoutMs: LEASE_MS })
+    expect(result?.providerFailure).toBe('provider_limit')
+    expect(result?.timedOut).toBeUndefined()
+  })
+
+  it('measures the command deadline from dispatch, after a slow ownership write', async () => {
+    cappedPlane(CAP_MS - 30_000)
+    pause.mockRejectedValueOnce(new Error('pause unavailable'))
+    const sandbox = await e2bProvider.findSessionSandbox?.('chat', { lifetimeMs: LEASE_MS })
+    if (!sandbox) throw new Error('Missing sandbox')
+    const realNow = Date.now
+    let ownershipWriteMs = 0
+    const clock = vi.spyOn(Date, 'now').mockImplementation(() => realNow() + ownershipWriteMs)
+    try {
+      const result = await observeSandboxExecution(
+        {
+          hold: vi.fn(),
+          unsettled: vi.fn(),
+          claimProcess: async () => {
+            ownershipWriteMs = 2_000
+          },
+        },
+        () => sandbox.runCommand('long job', { timeoutMs: 29_000 })
+      )
+      expect(result.providerFailure).toBe('provider_limit')
+    } finally {
+      clock.mockRestore()
+    }
+  })
+
+  it('keeps a command that reaches its own timeout near the cap a user timeout', async () => {
+    cappedPlane(CAP_MS - 50_000)
+    pause.mockRejectedValueOnce(new Error('pause unavailable'))
+    const sandbox = await e2bProvider.findSessionSandbox?.('chat', { lifetimeMs: LEASE_MS })
+    const result = await sandbox?.runCommand('short job', { timeoutMs: 1000 })
+    expect(result?.providerFailure).toBeUndefined()
+    expect(result?.timedOut).toBe(true)
+  })
+})
@@ -106,7 +106,10 @@ const MATERIALIZER_REVISION_RADIX = 1000
 /** Public provider alias used by builder/task tests and release tooling. */
 export const E2B_SANDBOX_MATERIALIZER_REVISION = FUNCTION_SANDBOX_MATERIALIZER_REVISION
 
-/** Maximum continuous sandbox lifetime supported by E2B. */
+/**
+ * E2B's continuous-runtime cap on the Pro tier: a running sandbox is killed this long after it
+ * last started or resumed, however long its timeout says, and a pause plus resume resets the count.
+ */
 export const E2B_MAX_SANDBOX_LIFETIME_MS = 24 * 60 * 60 * 1000
 
 /** E2B sends sandbox lifetimes as whole seconds. */
@@ -164,14 +167,17 @@ function prepareE2BCommand(
   }
 }
 
+/** Only a command whose own timeout would outlive the cap can have been ended by it. */
 function reachedE2BProviderLimit(
   error: unknown,
-  providerLimitAtMs: number | undefined,
+  providerLimitAtMs: number,
+  commandDeadlineAtMs: number | undefined,
   signal?: AbortSignal
 ): boolean {
   return (
     !signal?.aborted &&
-    providerLimitAtMs !== undefined &&
+    commandDeadlineAtMs !== undefined &&
+    commandDeadlineAtMs >= providerLimitAtMs &&
     Date.now() >= providerLimitAtMs - E2B_PROVIDER_LIMIT_CLASSIFICATION_WINDOW_MS &&
     isE2BExecutionTimeout(error)
   )
@@ -358,19 +364,30 @@ export async function stopE2BSessionProcess(
 class E2BSandboxHandle implements SandboxHandle {
   private killed = false
   private killPromise: Promise<void> | null = null
+  private sessionDeadlineAtMs?: number
 
   /**
+   * @param providerLimitAtMs No later than E2B's continuous-runtime cap for this sandbox, which no
+   *   timeout request can extend past.
    * @param sessionDeadlineAtMs Earliest time the provider can reap this session sandbox, as set
-   *   by this handle's own create, connect, or timeout request. Session deadlines only ever move
-   *   later — every update path extends and none shortens — so it stays a valid lower bound.
+   *   by this handle's own create, connect, or timeout request and never past the cap. Session
+   *   deadlines only ever move later — every update path extends and none shortens — so it stays
+   *   a valid lower bound.
    */
   constructor(
     private readonly sandbox: E2BSandbox,
     private readonly language: CodeLanguage,
-    private readonly providerLimitAtMs?: number,
+    private readonly providerLimitAtMs: number,
     private readonly sessionKey?: string,
-    private sessionDeadlineAtMs?: number
-  ) {}
+    sessionDeadlineAtMs?: number
+  ) {
+    if (sessionDeadlineAtMs !== undefined) this.recordSessionDeadline(sessionDeadlineAtMs)
+  }
+
+  /** E2B clamps every timeout to the cap, so no granted lease reaches past it. */
+  private recordSessionDeadline(atMs: number): void {
+    this.sessionDeadlineAtMs = Math.min(atMs, this.providerLimitAtMs)
+  }
 
   get sandboxId(): string {
     return this.sandbox.sandboxId
@@ -393,7 +410,7 @@ class E2BSandboxHandle implements SandboxHandle {
     }
     const requestedAtMs = Date.now()
     await this.sandbox.setTimeout(timeoutMs)
-    if (this.sessionKey !== undefined) this.sessionDeadlineAtMs = requestedAtMs + timeoutMs
+    if (this.sessionKey !== undefined) this.recordSessionDeadline(requestedAtMs + timeoutMs)
   }
 
   async runCode(
@@ -484,6 +501,7 @@ class E2BSandboxHandle implements SandboxHandle {
     operation: 'code' | 'command'
   ): Promise<SandboxCommandResult> {
     if (this.sessionKey !== undefined) options.signal?.throwIfAborted()
+    let commandDeadlineAtMs: number | undefined
     const outputBudget = new SandboxProcessOutputBudget(
       options.maxOutputBytes ?? MAX_SANDBOX_PROCESS_OUTPUT_BYTES
     )
@@ -553,6 +571,8 @@ class E2BSandboxHandle implements SandboxHandle {
       }
       let started: Awaited<ReturnType<E2BSandbox['commands']['run']>>
       try {
+        /** E2B starts the process timeout at dispatch, after the ownership write above. */
+        commandDeadlineAtMs = Date.now() + processOptions.timeoutMs
         started = await this.sandbox.commands.run(
           processId
             ? sessionProcessCommand(processId, prepared.command, options.rootUser)
@@ -662,7 +682,9 @@ class E2BSandboxHandle implements SandboxHandle {
       if (outputBudget.error) throw outputBudget.error
       if (isSandboxOutputLimitError(error)) throw error
       if (isNonRetryableExecutionError(error)) throw error
-      if (reachedE2BProviderLimit(error, this.providerLimitAtMs, options.signal)) {
+      if (
+        reachedE2BProviderLimit(error, this.providerLimitAtMs, commandDeadlineAtMs, options.signal)
+      ) {
         recordSandboxProviderLimit({ provider: 'e2b', operation })
         return {
           stdout: '',
@@ -1085,9 +1107,7 @@ export const e2bProvider: SandboxProvider = {
     return new E2BSandboxHandle(
       sandbox,
       options?.language ?? CodeLanguage.Python,
-      effectiveLifetimeMs === E2B_MAX_SANDBOX_LIFETIME_MS
-        ? lifetimeStartedAtMs + E2B_MAX_SANDBOX_LIFETIME_MS
-        : undefined,
+      lifetimeStartedAtMs + E2B_MAX_SANDBOX_LIFETIME_MS,
       options?.sessionKey,
       options?.sessionKey && effectiveLifetimeMs !== undefined
         ? lifetimeStartedAtMs + effectiveLifetimeMs
@@ -1116,19 +1136,38 @@ export const e2bProvider: SandboxProvider = {
         'This workbench predates durable execution ownership and requires recovery before reuse'
       )
     }
+    const leaseMs = options.lifetimeMs === undefined ? 0 : e2bTimeoutMs(options.lifetimeMs)
+    let resuming = candidate.state === 'paused'
+    // E2B silently clamps any timeout to its continuous-runtime cap. A pause plus resume restarts
+    // that count with memory, files, and processes intact, where a new workbench would lose them.
+    if (
+      !resuming &&
+      Date.now() + leaseMs > candidate.startedAt.getTime() + E2B_MAX_SANDBOX_LIFETIME_MS
+    ) {
+      try {
+        await Sandbox.pause(candidate.sandboxId, { apiKey })
+        resuming = true
+      } catch (error) {
+        logger.warn(
+          'Failed to pause workbench to reset its runtime cap; reusing it until the cap',
+          {
+            sandboxId: candidate.sandboxId,
+            error: getErrorMessage(error),
+          }
+        )
+      }
+    }
     // Connect also sets a timeout, including for running sandboxes. Preserve the active deadline,
     // and grant the requested lease in the same request instead of a later getInfo + setTimeout.
     const requestedAtMs = Date.now()
-    const timeoutMs = Math.max(
-      5 * 60_000,
-      candidate.endAt.getTime() - requestedAtMs,
-      options.lifetimeMs === undefined ? 0 : e2bTimeoutMs(options.lifetimeMs)
-    )
+    const timeoutMs = Math.max(5 * 60_000, candidate.endAt.getTime() - requestedAtMs, leaseMs)
+    const providerLimitAtMs =
+      (resuming ? requestedAtMs : candidate.startedAt.getTime()) + E2B_MAX_SANDBOX_LIFETIME_MS
     const sandbox = await Sandbox.connect(candidate.sandboxId, { apiKey, timeoutMs })
     return new E2BSandboxHandle(
       sandbox,
       options.language ?? CodeLanguage.Python,
-      undefined,
+      providerLimitAtMs,
       key,
       options.lifetimeMs === undefined ? undefined : requestedAtMs + timeoutMs
     )
 
@@ -97,6 +97,29 @@ it('bounds the remote copy itself, not just the eventual response stream', async
   ).rejects.toThrow('size limit')
   expect(mocks.read).not.toHaveBeenCalled()
 })
+it('asks the reconnect for the idle lease, which can outlast the runtime cap', async () => {
+  const IDLE_MS = 20 * 60_000
+  const capAtMs = Date.now() + 60_000
+  let leaseEndAtMs = capAtMs
+  const machine = await mocks.find()
+  mocks.find.mockImplementation(async (_key: string, options: { lifetimeMs?: number }) => {
+    if (options.lifetimeMs !== undefined) leaseEndAtMs = Date.now() + options.lifetimeMs
+    return {
+      ...machine,
+      extendLifetime: async (lifetimeMs: number) => {
+        leaseEndAtMs = Math.min(Date.now() + lifetimeMs, capAtMs)
+      },
+    }
+  })
+  const path = join(directory, 'source.txt')
+  await writeFile(path, 'original')
+  const snapshot = await openSessionFileSnapshot('chat', path, undefined, undefined, {
+    allowedRoots: [directory],
+    maxBytes: 100,
+  })
+  await snapshot.dispose()
+  expect(leaseEndAtMs).toBeGreaterThanOrEqual(Date.now() + IDLE_MS - 1000)
+})
 it('never creates a replacement machine for a missing read', async () => {
   mocks.find.mockResolvedValue(null)
   await expect(openSessionFileSnapshot('chat', '/tmp/missing')).rejects.toThrow(
 
@@ -61,7 +61,10 @@ export async function openSessionFileSnapshot(
   try {
     return await withSandboxSessionLock(sessionKey, signal, async (accessSignal) => {
       const provider = resolveProvider()
-      const sandbox = await provider.findSessionSandbox?.(sessionKey, {})
+      // The reconnect grants the idle lease itself, so it can reset a workbench near its runtime cap.
+      const sandbox = await provider.findSessionSandbox?.(sessionKey, {
+        lifetimeMs: SESSION_SANDBOX_IDLE_MS,
+      })
       accessSignal.throwIfAborted()
       if (!sandbox) throw new Error(`No workbench exists for this chat; write "${path}" first.`)
       const readStream = sandbox.readFileStream?.bind(sandbox)
@@ -84,7 +87,6 @@ export async function openSessionFileSnapshot(
         return disposed
       }
       try {
-        await sandbox.extendLifetime?.(SESSION_SANDBOX_IDLE_MS)
         accessSignal.throwIfAborted()
         const copied = await sandbox.runCommand(COPY_FILE, {
           envs: {
 
@@ -83,6 +83,23 @@ describe('workbench file cancellation', () => {
     })
   })
 
+  it('asks the reconnect for the idle lease, which can outlast the runtime cap', async () => {
+    const IDLE_MS = 20 * 60_000
+    const capAtMs = Date.now() + 60_000
+    let leaseEndAtMs = capAtMs
+    find.mockImplementation(async (_key: string, options: { lifetimeMs?: number }) => {
+      if (options.lifetimeMs !== undefined) leaseEndAtMs = Date.now() + options.lifetimeMs
+      return {
+        readFileWithLimit: read,
+        extendLifetime: async (lifetimeMs: number) => {
+          leaseEndAtMs = Math.min(Date.now() + lifetimeMs, capAtMs)
+        },
+      }
+    })
+    expect(await readSessionSandboxFile('chat', 'input.txt')).toMatchObject({ outcome: 'read' })
+    expect(leaseEndAtMs).toBeGreaterThanOrEqual(Date.now() + IDLE_MS - 1000)
+  })
+
   it('does not write if Stop arrives during the sandbox lookup', async () => {
     const controller = new AbortController()
     find.mockImplementation(async () => {