fix(statusline): unset a stale user statusline var, write the exporter script atomically

Three small follow-ups from the #361 review.

A tmux setenv survives respawn-pane, so _configureStatusLineUserCommand
returning early when the user has no statusline left a previously
exported CODEMAN_USER_STATUSLINE_CMD in place: a user who deleted their
own statusline kept getting the stale one wrapped, and lost Codeman's
footer print-through, until the tmux session was recreated. It now
issues `setenv -u` in that case, the same shape as the effort-level
cleanup in applyEnvOverrides.

ensureStatusLineExporterScript truncated and rewrote a script that live
sessions execute on every statusline render, and chmod'd it after the
write. It now writes a temp file next to the target, chmods that, and
rename()s it into place.

The non-tmux direct-PTY fallback carries no exporter; that is now stated
at the spawn site and in the architecture-invariants paragraph rather
than left as a silent gap.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

test/hooks-config.test.ts

@@ -17,6 +17,7 @@ import {
   rmSync,
   symlinkSync,
   statSync,
+  readdirSync,
 } from 'node:fs';
 import { join } from 'node:path';
 import { SETTINGS_PATH } from '../src/web/route-helpers.js';
@@ -1403,6 +1404,20 @@ describe('resolveStatusLineCliCommand', () => {
     expect(readFileSync(cmd!, 'utf-8')).toContain('CODEMAN_STATUSLINE_EXPORTER_V');
   });
 
+  it('refreshes a stale exporter script atomically: executable on arrival, no temp file left behind', async () => {
+    const scriptPath = (await resolveStatusLineCliCommand(testDir, true))!;
+    // Simulate a script an older build wrote (different marker suffix).
+    writeFileSync(scriptPath, '#!/bin/sh\n# CODEMAN_STATUSLINE_EXPORTER_V0\necho stale\n');
+    chmodSync(scriptPath, 0o644);
+
+    const again = await resolveStatusLineCliCommand(testDir, true);
+    expect(again).toBe(scriptPath);
+    expect(readFileSync(scriptPath, 'utf-8')).not.toContain('echo stale');
+    expect(statSync(scriptPath).mode & 0o111).not.toBe(0);
+    const siblings = readdirSync(join(scriptPath, '..')).filter((f) => f.startsWith('statusline-exporter.sh.'));
+    expect(siblings).toEqual([]);
+  });
+
   it('never overrides a real, hand-authored statusLine', async () => {
     const claudeDir = join(testDir, '.claude');
     mkdirSync(claudeDir, { recursive: true });

test/tmux-manager.test.ts

@@ -99,6 +99,32 @@ describe('TmuxManager (unit)', () => {
     });
   });
 
+  describe('statusline user-command env', () => {
+    // A tmux setenv survives respawn-pane, so the absence of a user statusline
+    // must UNSET the variable rather than leave a stale one for the exporter
+    // to wrap.
+    it('unsets CODEMAN_USER_STATUSLINE_CMD when the user has no statusline', () => {
+      mockedExecSync.mockClear();
+      (
+        manager as unknown as { _configureStatusLineUserCommand: (m: string, c?: string) => void }
+      )._configureStatusLineUserCommand('codeman-abc', undefined);
+      const cmds = mockedExecSync.mock.calls.map((c) => String(c[0]));
+      expect(cmds.some((c) => c.includes("setenv -t 'codeman-abc' -u CODEMAN_USER_STATUSLINE_CMD"))).toBe(true);
+    });
+
+    it('sets CODEMAN_USER_STATUSLINE_CMD, shell-escaped, when the user has one', () => {
+      mockedExecSync.mockClear();
+      (
+        manager as unknown as { _configureStatusLineUserCommand: (m: string, c?: string) => void }
+      )._configureStatusLineUserCommand('codeman-abc', `printf '%s' "$1" | jq -r .model`);
+      const cmds = mockedExecSync.mock.calls.map((c) => String(c[0]));
+      const setCmd = cmds.find((c) => c.includes('CODEMAN_USER_STATUSLINE_CMD'));
+      expect(setCmd).toBeDefined();
+      expect(setCmd).not.toContain(' -u ');
+      expect(setCmd).toContain("setenv -t 'codeman-abc' CODEMAN_USER_STATUSLINE_CMD ");
+    });
+  });
+
   describe('Codex command builder', () => {
     it('controls decorative TUI animation through Codex config', () => {
       expect(buildCodexCommand({ animations: false })).toBe('codex --config tui.animations=false');