Harden credential handling in shell snapshots and replay (#44040)

## Why

Shell quoting can hide credentials from raw-text checks, and startup files can restore real credentials after the broker replaces them with dummy values.

## What changed

- Decode shell literals without evaluating them and reject snapshots containing credentials in executable source, including aliases, functions, and heredocs.
- Preserve credential policy overrides, explicit unsets, and aliases whose source variables were removed. Support credential aliases in Zsh tied arrays while rejecting credentials that span array elements.
- Guard snapshot replay against credential restoration through shell startup files and preserve unrelated `ENV` settings.
- Apply Windows environment-key casing rules to credential overrides, suppress unredacted sandbox diagnostics during snapshot capture, and clear inherited environment variables before launching escalated commands.

## Testing

Add regression coverage for shell quoting and escaped credentials, Zsh tied arrays, startup-file replay, readonly credentials, policy overrides, and sensitive capture timeout and cancellation handling.

GitOrigin-RevId: 58274c07c715423241d26ce6dd2c2b4230cf0f64

codex-rs/shell-command/src/shell_snapshot.rs

@@ -6,6 +6,8 @@ mod capture;
 mod credentials;
 #[path = "shell_snapshot_exports.rs"]
 mod exports;
+#[path = "shell_snapshot_literals.rs"]
+mod literals;
 #[path = "shell_snapshot_render.rs"]
 mod render;
 
@@ -17,6 +19,8 @@ pub use credentials::PreparedSnapshot;
 pub use credentials::SnapshotCredentialEnvironment;
 pub use credentials::prepare_snapshot_credentials;
 
+use capture::BASH_SH_SNAPSHOT_HEADER;
+
 #[cfg(all(test, unix))]
 #[path = "shell_snapshot_tests.rs"]
 mod tests;