diff --git a/src/main/browser/agent-browser-bridge-execution.ts b/src/main/browser/agent-browser-bridge-execution.ts
index a2f11fce47a..31f5a191ede 100644
--- a/src/main/browser/agent-browser-bridge-execution.ts
+++ b/src/main/browser/agent-browser-bridge-execution.ts
@@ -176,7 +176,6 @@ export abstract class AgentBrowserBridgeExecution extends AgentBrowserBridgeTabs
   protected closeStaleAgentBrowserSession(sessionName: string): Promise<void> {
     if (
       canSkipAgentBrowserSessionReset({
-        platform: process.platform,
         ownsSocketDirectory: this.ownsAgentBrowserSocketDirectory,
         socketDirectory: this.agentBrowserEnv.AGENT_BROWSER_SOCKET_DIR,
         sessionName
diff --git a/src/main/browser/agent-browser-bridge-session-lifecycle.test.ts b/src/main/browser/agent-browser-bridge-session-lifecycle.test.ts
index 0b028538c8a..2955cb66263 100644
--- a/src/main/browser/agent-browser-bridge-session-lifecycle.test.ts
+++ b/src/main/browser/agent-browser-bridge-session-lifecycle.test.ts
@@ -81,6 +81,14 @@ function closeCallCount(): number {
 describe('AgentBrowserBridge', () => {
   let bridge: AgentBrowserBridge
 
+  // The mocked fs has no mkdirSync, so the constructor never claims a socket directory itself.
+  function ownSocketDirectory(): void {
+    Object.assign(bridge, {
+      ownsAgentBrowserSocketDirectory: true,
+      agentBrowserEnv: { AGENT_BROWSER_SOCKET_DIR: '/tmp/orca-ab-test' }
+    })
+  }
+
   beforeEach(() => {
     resetAgentBrowserBridgeMocks({
       webContentsFromIdMock,
@@ -89,35 +97,28 @@ describe('AgentBrowserBridge', () => {
       stdinWrites,
       cdpWsProxyInstances: CdpWsProxyMock.instances
     })
+    // Default to a socket that exists so an unprepared test still takes the reset path.
+    lstatSyncMock.mockReset()
+    lstatSyncMock.mockReturnValue({})
     bridge = new AgentBrowserBridge(mockBrowserManager())
     bridge.setActiveTab(100)
   })
 
   it('snapshots a fresh owned session without launching a helper just to close it', async () => {
-    vi.spyOn(process, 'platform', 'get').mockReturnValue('darwin')
-    Object.assign(bridge, {
-      ownsAgentBrowserSocketDirectory: true,
-      agentBrowserEnv: { AGENT_BROWSER_SOCKET_DIR: '/tmp/orca-ab-test' }
-    })
+    ownSocketDirectory()
     lstatSyncMock.mockImplementation(() => {
       throw Object.assign(new Error('No socket'), { code: 'ENOENT' })
     })
     webContentsFromIdMock.mockReturnValue(mockWebContents(100))
     succeedWith({ snapshot: 'ready' })
 
-    try {
-      expect(await bridge.snapshot()).toMatchObject({ snapshot: 'ready' })
-      expect(closeCallCount()).toBe(0)
-    } finally {
-      vi.restoreAllMocks()
-    }
+    expect(await bridge.snapshot()).toMatchObject({ snapshot: 'ready' })
+    expect(closeCallCount()).toBe(0)
+    expect(lstatSyncMock).toHaveBeenCalledWith('/tmp/orca-ab-test/orca-tab-tab-1.sock')
   })
 
   it('fails closed when stale agent-browser session ownership cannot be reset', async () => {
-    Object.assign(bridge, {
-      ownsAgentBrowserSocketDirectory: true,
-      agentBrowserEnv: { AGENT_BROWSER_SOCKET_DIR: '/tmp/orca-ab-test' }
-    })
+    ownSocketDirectory()
     lstatSyncMock.mockReturnValue({})
     vi.useFakeTimers()
     try {
diff --git a/src/main/browser/agent-browser-session-reset.test.ts b/src/main/browser/agent-browser-session-reset.test.ts
index 974fa348cc9..b38822d5175 100644
--- a/src/main/browser/agent-browser-session-reset.test.ts
+++ b/src/main/browser/agent-browser-session-reset.test.ts
@@ -6,27 +6,28 @@ vi.mock('node:fs', () => ({ lstatSync }))
 import { canSkipAgentBrowserSessionReset } from './agent-browser-session-reset'
 
 const owned = {
-  platform: 'darwin' as const,
   ownsSocketDirectory: true,
   socketDirectory: '/tmp/orca-ab-profile',
   sessionName: 'orca-tab-page'
 }
+const socketPath = join(owned.socketDirectory, 'orca-tab-page.sock')
 
 beforeEach(() => {
   lstatSync.mockReset()
 })
 
-it.each(['darwin', 'linux'] as const)('skips an absent owned socket on %s', (platform) => {
+it('skips an absent owned socket', () => {
   lstatSync.mockImplementation(() => {
     throw Object.assign(new Error('No socket'), { code: 'ENOENT' })
   })
-  expect(canSkipAgentBrowserSessionReset({ ...owned, platform })).toBe(true)
-  expect(lstatSync).toHaveBeenCalledWith(join(owned.socketDirectory, 'orca-tab-page.sock'))
+  expect(canSkipAgentBrowserSessionReset(owned)).toBe(true)
+  expect(lstatSync).toHaveBeenCalledWith(socketPath)
 })
 
 it('requires reset when a socket or symlink exists', () => {
   lstatSync.mockReturnValue({})
   expect(canSkipAgentBrowserSessionReset(owned)).toBe(false)
+  expect(lstatSync).toHaveBeenCalledWith(socketPath)
 })
 
 it.each(['EACCES', 'EIO', 'ENOTDIR'])('requires reset for %s', (code) => {
@@ -34,14 +35,15 @@ it.each(['EACCES', 'EIO', 'ENOTDIR'])('requires reset for %s', (code) => {
     throw Object.assign(new Error('Socket inspection failed'), { code })
   })
   expect(canSkipAgentBrowserSessionReset(owned)).toBe(false)
+  expect(lstatSync).toHaveBeenCalledWith(socketPath)
 })
 
+// Windows and inherited socket directories both arrive as ownsSocketDirectory: false.
 it.each([
-  { platform: 'win32' as const },
   { ownsSocketDirectory: false },
   { socketDirectory: undefined },
-  { socketDirectory: 'relative' },
   { sessionName: '../other' },
+  { sessionName: 'has space' },
   { sessionName: '' }
 ])('requires reset without an owned Unix socket address: %j', (override) => {
   expect(canSkipAgentBrowserSessionReset({ ...owned, ...override })).toBe(false)
diff --git a/src/main/browser/agent-browser-session-reset.ts b/src/main/browser/agent-browser-session-reset.ts
index a6240c03612..8c6b7545f02 100644
--- a/src/main/browser/agent-browser-session-reset.ts
+++ b/src/main/browser/agent-browser-session-reset.ts
@@ -1,28 +1,30 @@
 import { lstatSync } from 'node:fs'
-import { basename, isAbsolute, join } from 'node:path'
+import { join } from 'node:path'
 
+// agent-browser's own session-name rule; doubles as a traversal fence for the `join` below.
+const SAFE_SESSION_NAME = /^[A-Za-z0-9_-]+$/
+
+/**
+ * True when no daemon can be holding `sessionName`, so closing it would only start one.
+ *
+ * Only an Orca-derived socket directory proves that (`ownsSocketDirectory`): it is a
+ * private per-profile `/tmp` directory, never an inherited one shared with a second
+ * profile, and never Windows, which uses named pipes and leaves no socket to inspect.
+ */
 export function canSkipAgentBrowserSessionReset(options: {
-  platform: NodeJS.Platform
   ownsSocketDirectory: boolean
   socketDirectory: string | undefined
   sessionName: string
 }): boolean {
   const { socketDirectory, sessionName } = options
-  if (
-    options.platform === 'win32' ||
-    !options.ownsSocketDirectory ||
-    !socketDirectory ||
-    !isAbsolute(socketDirectory) ||
-    !sessionName ||
-    basename(sessionName) !== sessionName
-  ) {
+  if (!options.ownsSocketDirectory || !socketDirectory || !SAFE_SESSION_NAME.test(sessionName)) {
     return false
   }
   try {
     lstatSync(join(socketDirectory, `${sessionName}.sock`))
     return false
   } catch (error) {
-    // An absent owned socket cannot be reused; permission and other failures prove nothing.
+    // Only a proven-absent socket is safe to skip; permission and other failures prove nothing.
     return (error as NodeJS.ErrnoException).code === 'ENOENT'
   }
 }