From 49754620392f8763ef5b3eea42f154a74a5ae30f Mon Sep 17 00:00:00 2001
From: Codex Review <codex-review@example.com>
Date: Sat, 18 Apr 2026 08:47:00 +0000
Subject: [PATCH] Preserve POSIX tmux preflight on MSYS2 Windows shells

The first #2711 fix correctly stopped native Windows shells from receiving
Unix-only exec wrapping, but the preflight path in runClaudeOutsideTmux
still keyed off process.platform alone. That caused MSYS2/Git Bash sessions
on Windows to skip the existing POSIX sleep/tcflush preflight even though
they still use login-shell wrapping.

Constraint: Keep native Windows COMSPEC handling intact
Constraint: Preserve existing POSIX/MSYS2 login-shell behavior without broad launch refactors
Rejected: Revert the Windows-specific path entirely | would reintroduce the original PowerShell failure
Rejected: Add separate MSYS2-specific launch branches everywhere | broader drift than needed
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: When branching shell launch behavior, key off native-Windows-vs-POSIX shell semantics, not process.platform by itself
Tested: npm test -- --run src/cli/__tests__/tmux-utils.test.ts src/cli/__tests__/launch.test.ts src/cli/__tests__/autoresearch-guided.test.ts
Tested: npm run build:cli
Not-tested: Live tmux launch on a real MSYS2/Git Bash Windows host
Related: #2711
Related: #2713
---
 bridge/cli.cjs                   |  2 +-
 src/cli/__tests__/launch.test.ts | 16 ++++++++++++++++
 src/cli/launch.ts                |  2 +-
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/bridge/cli.cjs b/bridge/cli.cjs
index 57027aa3..e15871f8 100755
--- a/bridge/cli.cjs
+++ b/bridge/cli.cjs
@@ -85582,7 +85582,7 @@ function runClaudeOutsideTmux(cwd2, args, _sessionId) {
   );
   const rawClaudeCmd = isNativeWindowsShell() ? buildTmuxShellCommandWithEnv("claude", args, forwardedEnv) : buildTmuxShellCommand("claude", args);
   const envPrefix = !isNativeWindowsShell() && Object.keys(forwardedEnv).length > 0 ? buildEnvExportPrefix(TMUX_ENV_FORWARD) : "";
-  const preflight = process.platform === "win32" ? envPrefix : `${envPrefix}sleep 0.3; perl -e 'use POSIX;tcflush(0,TCIFLUSH)' 2>/dev/null; `;
+  const preflight = isNativeWindowsShell() ? envPrefix : `${envPrefix}sleep 0.3; perl -e 'use POSIX;tcflush(0,TCIFLUSH)' 2>/dev/null; `;
   const claudeCmd = wrapWithLoginShell(`${preflight}${rawClaudeCmd}`);
   const sessionName2 = buildTmuxSessionName(cwd2);
   try {
diff --git a/src/cli/__tests__/launch.test.ts b/src/cli/__tests__/launch.test.ts
index bfe437eb..0caccacc 100644
--- a/src/cli/__tests__/launch.test.ts
+++ b/src/cli/__tests__/launch.test.ts
@@ -1245,4 +1245,20 @@ describe('runClaude outside-tmux — env forwarding', () => {
 
     Object.defineProperty(process, 'platform', { value: originalPlatform, configurable: true });
   });
+
+  it('keeps POSIX preflight commands on MSYS2 Windows shells', () => {
+    const originalPlatform = process.platform;
+    Object.defineProperty(process, 'platform', { value: 'win32', configurable: true });
+    process.env.CLAUDE_CONFIG_DIR = '/custom/config';
+    vi.mocked(isNativeWindowsShell).mockReturnValue(false);
+
+    runClaude('/tmp', ['--print-system-prompt', 'hello world'], 'sid');
+
+    const rawCommand = vi.mocked(wrapWithLoginShell).mock.calls[0][0];
+    expect(rawCommand).toContain('export CLAUDE_CONFIG_DIR=/custom/config');
+    expect(rawCommand).toContain('sleep 0.3');
+    expect(rawCommand).toContain("perl -e 'use POSIX;tcflush(0,TCIFLUSH)' 2>/dev/null;");
+
+    Object.defineProperty(process, 'platform', { value: originalPlatform, configurable: true });
+  });
 });
diff --git a/src/cli/launch.ts b/src/cli/launch.ts
index efd43524..4e53664d 100644
--- a/src/cli/launch.ts
+++ b/src/cli/launch.ts
@@ -476,7 +476,7 @@ function runClaudeOutsideTmux(cwd: string, args: string[], _sessionId: string):
   // A short sleep lets the response arrive, then tcflush discards it.
   // Wrap in login shell so .bashrc/.zshrc are sourced (PATH, nvm, etc.)
   // Env exports are injected after RC sourcing so they override stale tmux server env.
-  const preflight = process.platform === 'win32'
+  const preflight = isNativeWindowsShell()
     ? envPrefix
     : `${envPrefix}sleep 0.3; perl -e 'use POSIX;tcflush(0,TCIFLUSH)' 2>/dev/null; `;
   const claudeCmd = wrapWithLoginShell(`${preflight}${rawClaudeCmd}`);