fix(platform): in the Flatpak a pass's shell is bash

Flatpak sets SHELL to /bin/sh, the host's (zsh here) being no file of
the Sdk's, and claude's Bash tool runs commands with bash or zsh. In the
sandbox SHELL becomes /bin/bash unless it names a bash or zsh that is
there. Found by the sandbox checks: a pass's environment had SHELL=/bin/sh.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

implementations/Crafter.Review-Platform.cpp

@@ -65,7 +65,10 @@ namespace Crafter::Review::Platform {
 
     void Init() {
         CurrentModeValue = fs::exists(PathsValue().flatpakInfo) ? Mode::Sandbox : Mode::Native;
-        if (CurrentModeValue == Mode::Sandbox) RestoreHostXdg();
+        if (CurrentModeValue == Mode::Sandbox) {
+            RestoreHostXdg();
+            RestoreShell();
+        }
     }
 
     Mode CurrentMode() {
@@ -128,6 +131,12 @@ namespace Crafter::Review::Platform {
         }
     }
 
+    void RestoreShell() {
+        const std::string shell = GetEnv("SHELL").value_or("");
+        const bool usable = (shell.ends_with("/bash") || shell.ends_with("/zsh")) && access(shell.c_str(), X_OK) == 0;
+        if (!usable && access("/bin/bash", X_OK) == 0) setenv("SHELL", "/bin/bash", 1);
+    }
+
     fs::path SelfExe() {
         std::error_code error;
         const fs::path exe = fs::read_symlink("/proc/self/exe", error);

interfaces/Crafter.Review-Platform.cppm

@@ -51,6 +51,11 @@ export namespace Crafter::Review::Platform {
     // $HOME), so git reads ~/.config/git/config, Playwright finds
     // ~/.cache/ms-playwright, and claude and npx behave as on the host.
     void RestoreHostXdg();
+    // Flatpak sets SHELL to /bin/sh, the host's (zsh here) being no file of
+    // the Sdk's. claude's Bash tool runs commands with bash or zsh, and the
+    // Sdk has bash: SHELL becomes /bin/bash unless it already names a bash
+    // or zsh that is there.
+    void RestoreShell();
     // The absolute path of the running binary (/proc/self/exe).
     std::filesystem::path SelfExe();
 

tests/Platform/main.cpp

@@ -205,6 +205,21 @@ int main() {
         Check(Platform::GetEnv("XDG_CONFIG_HOME") == "/elsewhere/config", "a host XDG directory the host set comes back");
         Check(Platform::GetEnv("XDG_CACHE_HOME") == Dyn::JoinPath(home, ".cache"), "one it left unset is the XDG default under $HOME");
         Check(Platform::GetEnv("XDG_STATE_HOME") == Dyn::JoinPath(home, ".local/state"), "state too");
+        // The shell: the sandbox's /bin/sh becomes bash; a bash or zsh that is
+        // there stays.
+        const std::optional<std::string> shell = Platform::GetEnv("SHELL");
+        setenv("SHELL", "/bin/sh", 1);
+        Platform::RestoreShell();
+        const std::optional<std::string> fromSh = Platform::GetEnv("SHELL");
+        setenv("SHELL", "/no/such/zsh", 1);
+        Platform::RestoreShell();
+        const std::optional<std::string> fromMissing = Platform::GetEnv("SHELL");
+        setenv("SHELL", "/bin/bash", 1);
+        Platform::RestoreShell();
+        const std::optional<std::string> fromBash = Platform::GetEnv("SHELL");
+        if (shell) setenv("SHELL", shell->c_str(), 1);
+        Check(!fs::exists("/bin/bash") || (fromSh == "/bin/bash" && fromMissing == "/bin/bash" && fromBash == "/bin/bash"),
+              "SHELL: /bin/sh and a shell that is not there become /bin/bash; bash stays");
     }
 
     {