Carry shell invocation metadata and report executor PATH directories (#49360)

## What changed

- Carry the selected shell and login mode through unified exec using `ShellInvocation`. Use this metadata for shell snapshots and credential brokerage instead of inferring it from command arguments.
- Add `prependPathDirs` to exec-server environment metadata, populated from the executor's package PATH directory. Default to an empty list for older servers and omit empty lists from serialized output.

## Testing

Extend environment metadata round-trip coverage for `prependPathDirs` and the remote exec-server integration test to verify the packaged `codex-path` directory is reported.

GitOrigin-RevId: c571c068effcb305d196a701ad9a335ec7a3f5a2

codex-rs/core/src/unified_exec/mod.rs

@@ -43,7 +43,7 @@ use crate::session::session::Session;
 use crate::session::step_context::StepContext;
 use crate::session::turn_context::TurnContext;
 use crate::session::turn_context::TurnEnvironment;
-use crate::shell::ShellType;
+use crate::shell::ShellInvocation;
 use crate::tools::network_approval::DeferredNetworkApproval;
 use codex_core_plugins::PluginMetricsSidecar;
 
@@ -113,7 +113,7 @@ impl UnifiedExecContext {
 #[derive(Debug)]
 pub(crate) struct ExecCommandRequest {
     pub command: Vec<String>,
-    pub shell_type: ShellType,
+    pub shell: ShellInvocation,
     pub hook_command: String,
     pub process_id: i32,
     pub yield_time_ms: u64,

codex-rs/core/src/unified_exec/process_manager.rs

@@ -1505,7 +1505,7 @@ impl UnifiedExecProcessManager {
             .await;
         let req = UnifiedExecToolRequest {
             command: request.command.clone(),
-            shell_type: request.shell_type,
+            shell: request.shell.clone(),
             hook_command: request.hook_command.clone(),
             process_id: request.process_id,
             cwd,

codex-rs/core/src/unified_exec/process_manager_tests.rs

@@ -1,4 +1,7 @@
 use super::*;
+use crate::shell::Shell;
+use crate::shell::ShellInvocation;
+use crate::shell::ShellType;
 use crate::unified_exec::clamp_yield_time;
 use codex_network_proxy::ManagedNetworkSandboxContext;
 use core_test_support::assert_regex_match;
@@ -459,7 +462,13 @@ async fn failed_initial_end_for_unstored_process_uses_fallback_output() {
             "-lc".to_string(),
             "echo before".to_string(),
         ],
-        shell_type: crate::shell::ShellType::Sh,
+        shell: ShellInvocation {
+            shell: Shell {
+                shell_type: ShellType::Sh,
+                shell_path: "sh".into(),
+            },
+            use_login_shell: true,
+        },
         hook_command: "echo before".to_string(),
         process_id: 123,
         yield_time_ms: 1000,

codex-rs/core/src/unified_exec/shell_snapshot.rs

@@ -179,15 +179,12 @@ pub(super) fn shell_snapshot_request(
         || !request.turn_environment.shell_snapshot_v2_supported
         || request.turn_environment.selection.cwd != *cwd
         || !matches!(request.shell_mode, UnifiedExecShellMode::Direct)
-        || !matches!(
-            request.shell_type,
-            ShellType::Bash | ShellType::Zsh | ShellType::Sh
-        )
-        || request.command.get(1).is_none_or(|flag| flag != "-lc")
+        || !request.shell.is_posix_login()
     {
         return None;
     }
 
+    let shell = &request.shell.shell;
     Some(ShellSnapshotRequest {
         scope_id: format!(
             "{}:{}",
@@ -195,8 +192,8 @@ pub(super) fn shell_snapshot_request(
             request.turn_environment.selection.environment_id
         ),
         shell: ShellInfo {
-            name: request.shell_type.name().to_string(),
-            path: request.command.first()?.clone(),
+            name: shell.name().to_string(),
+            path: shell.shell_path.to_string_lossy().into_owned(),
         },
     })
 }