diff --git a/src/main/providers/filesystem-provider-contract.ts b/src/main/providers/filesystem-provider-contract.ts
index fb266bf1490..27dc5a6ec33 100644
--- a/src/main/providers/filesystem-provider-contract.ts
+++ b/src/main/providers/filesystem-provider-contract.ts
@@ -55,7 +55,8 @@ export type IFilesystemProvider = {
    *
    *  `position` must be a non-negative safe integer and `length` a positive one
    *  no larger than `MAX_FILE_RANGE_READ_BYTES`; anything else throws
-   *  `FileRangeReadRequestError` without reaching the host. */
+   *  `FileRangeReadRequestError` without reaching the host. The final byte
+   *  offset must also remain a safe integer. */
   readFileRange?(
     filePath: string,
     position: number,
diff --git a/src/main/providers/ssh-filesystem-provider-capabilities.test.ts b/src/main/providers/ssh-filesystem-provider-capabilities.test.ts
index 5a34b2a0c1f..66691119419 100644
--- a/src/main/providers/ssh-filesystem-provider-capabilities.test.ts
+++ b/src/main/providers/ssh-filesystem-provider-capabilities.test.ts
@@ -99,6 +99,31 @@ describe('SSH filesystem capability document', () => {
     expect(mux.request).toHaveBeenCalledTimes(1)
   })
 
+  it('retries when the fetch fails after its only waiter aborts', async () => {
+    let rejectFetch: (error: Error) => void = () => {}
+    const mux = {
+      request: vi
+        .fn()
+        .mockImplementationOnce(
+          () =>
+            new Promise((_resolve, reject) => {
+              rejectFetch = reject
+            })
+        )
+        .mockResolvedValue({ rangedReadVersion: 1 })
+    }
+    const controller = new AbortController()
+    const abandoned = probeSshRangedReadCapability(mux as never, controller.signal)
+    controller.abort()
+    await expect(abandoned).rejects.toThrow('client_disconnected')
+
+    rejectFetch(new Error('connection closed'))
+    await new Promise((resolve) => setImmediate(resolve))
+
+    await expect(probeSshRangedReadCapability(mux as never)).resolves.toBe(true)
+    expect(mux.request).toHaveBeenCalledTimes(2)
+  })
+
   it('treats a non-object response as no capabilities', async () => {
     const mux = { request: vi.fn().mockResolvedValue('yes') }
     await expect(probeSshRangedReadCapability(mux as never)).resolves.toBe(false)
diff --git a/src/main/providers/ssh-filesystem-provider-capabilities.ts b/src/main/providers/ssh-filesystem-provider-capabilities.ts
index 86451e5228b..2703c4d16c7 100644
--- a/src/main/providers/ssh-filesystem-provider-capabilities.ts
+++ b/src/main/providers/ssh-filesystem-provider-capabilities.ts
@@ -36,16 +36,13 @@ function readSshFsCapabilities(
       })
   if (!cached) {
     capabilitiesByMux.set(mux, probe)
-  }
-  return waitForSshCapabilityProbe(probe, signal).then(
-    (capabilities) => capabilities,
-    (error) => {
-      if (!signal?.aborted && capabilitiesByMux.get(mux) === probe) {
+    void probe.catch(() => {
+      if (capabilitiesByMux.get(mux) === probe) {
         capabilitiesByMux.delete(mux)
       }
-      throw error
-    }
-  )
+    })
+  }
+  return waitForSshCapabilityProbe(probe, signal)
 }
 
 export function probeSshQuickOpenSearchCapability(
diff --git a/src/main/providers/ssh-filesystem-provider-range.test.ts b/src/main/providers/ssh-filesystem-provider-range.test.ts
index a947d53845e..3dee006d59d 100644
--- a/src/main/providers/ssh-filesystem-provider-range.test.ts
+++ b/src/main/providers/ssh-filesystem-provider-range.test.ts
@@ -74,7 +74,8 @@ describe('SshFilesystemProvider.readFileRange', () => {
       ['a fractional position', 0.5, 4],
       ['a zero length', 0, 0],
       ['a negative length', 0, -1],
-      ['an over-cap length', 0, MAX_FILE_RANGE_READ_BYTES + 1]
+      ['an over-cap length', 0, MAX_FILE_RANGE_READ_BYTES + 1],
+      ['a window past safe-integer offsets', Number.MAX_SAFE_INTEGER, 2]
     ])('rejects %s without a round trip', async (_label, position, length) => {
       const request = vi.fn()
       await expect(
diff --git a/src/relay/fs-handler-file-range-dispatch.test.ts b/src/relay/fs-handler-file-range-dispatch.test.ts
index b408b6360da..3f1de4693a4 100644
--- a/src/relay/fs-handler-file-range-dispatch.test.ts
+++ b/src/relay/fs-handler-file-range-dispatch.test.ts
@@ -125,10 +125,7 @@ describe('fs.readFileRange over the real dispatcher', () => {
           0
         )
       )
-      for (let i = 0; i < 200 && frames.length === 0; i++) {
-        await new Promise((resolve) => setImmediate(resolve))
-      }
-      expect(frames).toHaveLength(1)
+      await vi.waitFor(() => expect(frames).toHaveLength(1), { timeout: 4_000 })
       const response = decodePayload(frames[0]) as {
         id: number
         error?: { code: number }
diff --git a/src/relay/fs-handler-file-range.test.ts b/src/relay/fs-handler-file-range.test.ts
index 4690b6a14c7..3ecca25ec4c 100644
--- a/src/relay/fs-handler-file-range.test.ts
+++ b/src/relay/fs-handler-file-range.test.ts
@@ -4,7 +4,11 @@ import { join } from 'node:path'
 import { afterEach, describe, expect, it } from 'vitest'
 import { readRelayFileRange } from './fs-handler-file-range'
 import { readFullStreamChunk } from './fs-handler-file-read'
-import { FileRangeReadRequestError, MAX_FILE_RANGE_READ_BYTES } from '../shared/file-range-read'
+import {
+  FileRangeReadRequestError,
+  MAX_FILE_RANGE_READ_BYTES,
+  validateFileRangeRequest
+} from '../shared/file-range-read'
 import { HEADER_LENGTH, prepareJsonRpcPayload } from './protocol'
 import { DISPATCHER_CONTROL_QUEUE_MAX_BYTES } from './dispatcher-writer-admission'
 
@@ -148,6 +152,7 @@ describe('readRelayFileRange', () => {
       ['a NaN position', Number.NaN, 4],
       ['an infinite position', Number.POSITIVE_INFINITY, 4],
       ['a position past the safe-integer range', Number.MAX_SAFE_INTEGER + 2, 4],
+      ['a window past the safe-integer range', Number.MAX_SAFE_INTEGER - 1, 3],
       ['a zero length', 0, 0],
       ['a negative length', 0, -4],
       ['a fractional length', 0, 4.5],
@@ -204,6 +209,22 @@ describe('readFullStreamChunk', () => {
     ])
   })
 
+  it('keeps every partial-read offset safe at the upper boundary', async () => {
+    const { position: start, length } = validateFileRangeRequest(Number.MAX_SAFE_INTEGER - 2, 3)
+    const calls: number[] = []
+    const reader = {
+      read(buffer: Buffer, offset: number, _length: number, position: number) {
+        calls.push(position)
+        buffer[offset] = 1
+        return Promise.resolve({ bytesRead: 1 })
+      }
+    }
+    const bytesRead = await readFullStreamChunk(reader, Buffer.alloc(length), length, start)
+    expect(bytesRead).toBe(length)
+    expect(calls).toEqual([start, start + 1, Number.MAX_SAFE_INTEGER])
+    expect(calls.every(Number.isSafeInteger)).toBe(true)
+  })
+
   // Without the zero check the loop would spin forever on a reader at EOF.
   it('stops at the first empty read and reports only what it filled', async () => {
     const source = Buffer.from('abcd')
diff --git a/src/shared/file-range-read.ts b/src/shared/file-range-read.ts
index 6af436fcf48..fe695e9a2c9 100644
--- a/src/shared/file-range-read.ts
+++ b/src/shared/file-range-read.ts
@@ -54,5 +54,8 @@ export function validateFileRangeRequest(
       `fs.readFileRange length ${length} exceeds the ${MAX_FILE_RANGE_READ_BYTES}-byte limit`
     )
   }
+  if (position > Number.MAX_SAFE_INTEGER - (length - 1)) {
+    throw new FileRangeReadRequestError('fs.readFileRange window exceeds safe-integer offsets')
+  }
   return { position, length }
 }