fix(tmux): preserve configured fallback port

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/features/tmux-subagent/manager.test.ts

@@ -3,7 +3,7 @@ import { describe, test, expect, mock, beforeEach, spyOn, afterAll } from 'bun:t
 import type { TmuxConfig } from '../../config/schema'
 import type { WindowState, PaneAction } from './types'
 import type { ActionResult, ExecuteContext } from './action-executor'
-import type { TmuxUtilDeps } from './manager'
+import type { TmuxSessionManager as TmuxSessionManagerType, TmuxUtilDeps } from './manager'
 import * as sharedModule from '../../shared'
 
 type ExecuteActionsResult = {
@@ -287,24 +287,67 @@ describe('TmuxSessionManager', () => {
 
     test('falls back to default port when serverUrl has port 0', async () => {
       // given
-      mockIsInsideTmux.mockReturnValue(true)
-      const { TmuxSessionManager } = await import('./manager')
-      const ctx = {
-        ...createMockContext(),
-        serverUrl: new URL('http://127.0.0.1:0/'),
-      }
-      const config = createTmuxConfig({ enabled: true,
-      layout: 'main-vertical',
-      main_pane_size: 60,
-      main_pane_min_width: 80,
-      agent_pane_min_width: 40, })
+      const previousOpenCodePort = process.env.OPENCODE_PORT
+      delete process.env.OPENCODE_PORT
+      let manager: TmuxSessionManagerType | undefined
+      try {
+        mockIsInsideTmux.mockReturnValue(true)
+        const { TmuxSessionManager } = await import('./manager')
+        const ctx = {
+          ...createMockContext(),
+          serverUrl: new URL('http://127.0.0.1:0/'),
+        }
+        const config = createTmuxConfig({ enabled: true,
+        layout: 'main-vertical',
+        main_pane_size: 60,
+        main_pane_min_width: 80,
+        agent_pane_min_width: 40, })
 
-      // when
-      const manager = new TmuxSessionManager(ctx, config, mockTmuxDeps)
+        // when
+        manager = new TmuxSessionManager(ctx, config, mockTmuxDeps)
+      } finally {
+        if (previousOpenCodePort === undefined) {
+          delete process.env.OPENCODE_PORT
+        } else {
+          process.env.OPENCODE_PORT = previousOpenCodePort
+        }
+      }
 
       // then
       expect((manager as any).serverUrl).toBe('http://localhost:4096')
     })
+
+    test('falls back to configured OPENCODE_PORT when serverUrl has port 0', async () => {
+      // given
+      const previousOpenCodePort = process.env.OPENCODE_PORT
+      process.env.OPENCODE_PORT = '5678'
+      let manager: TmuxSessionManagerType | undefined
+      try {
+        mockIsInsideTmux.mockReturnValue(true)
+        const { TmuxSessionManager } = await import('./manager')
+        const ctx = {
+          ...createMockContext(),
+          serverUrl: new URL('http://127.0.0.1:0/'),
+        }
+        const config = createTmuxConfig({ enabled: true,
+        layout: 'main-vertical',
+        main_pane_size: 60,
+        main_pane_min_width: 80,
+        agent_pane_min_width: 40, })
+
+        // when
+        manager = new TmuxSessionManager(ctx, config, mockTmuxDeps)
+      } finally {
+        if (previousOpenCodePort === undefined) {
+          delete process.env.OPENCODE_PORT
+        } else {
+          process.env.OPENCODE_PORT = previousOpenCodePort
+        }
+      }
+
+      // then
+      expect((manager as any).serverUrl).toBe('http://localhost:5678')
+    })
   })
 
   describe('onSessionCreated', () => {
@@ -1989,7 +2032,7 @@ describe('TmuxSessionManager', () => {
       const cleanupPromise = manager.cleanup()
 
       // then
-      await expect(cleanupPromise).resolves.toBeUndefined()
+      expect(await cleanupPromise).toBeUndefined()
       expect(mockKillTmuxSessionIfExists).toHaveBeenCalledTimes(1)
     })
   })

src/features/tmux-subagent/manager.ts

@@ -72,7 +72,8 @@ export class TmuxSessionManager {
     this.client = ctx.client
     this.tmuxConfig = tmuxConfig
     this.deps = deps
-    const fallbackUrl = "http://localhost:4096"
+    const defaultPort = process.env.OPENCODE_PORT ?? "4096"
+    const fallbackUrl = `http://localhost:${defaultPort}`
     const rawServerUrl = ctx.serverUrl?.toString()
     try {
       if (rawServerUrl) {