Replay exec-server shell snapshots through unnamed files (#48078)

## Why

Large shell snapshots need a replay path that does not add their state to the child process environment.

## What changed

- Keep captured state cached in memory and give each Bash or Zsh launch an independent, read-only file descriptor to source. Unlink the file before writing shell state, create it under the sandbox-protected daemon directory, and close the carrier descriptor before restoring functions.
- Probe descriptor-path access inside the capture sandbox. Retain environment replay for `sh` and when descriptor paths are unavailable; use normal shell startup if preparing the replay file fails.
- Group options and aliases during capture so sourcing preserves their parsing behavior.

## Testing

Add coverage for concurrent replays with 480 KiB payloads, pipe and TTY execution, stdin preservation, descriptor cleanup, sandbox protection, blocked descriptor-path fallback, and alias/option parsing equivalence.

GitOrigin-RevId: 8103d5c37ce4d1885628a4efba3551549f12bea8

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

@@ -42,6 +42,36 @@ pub struct SnapshotCaptureOptions {
 pub fn snapshot_capture_script(
     shell_type: ShellType,
     options: SnapshotCaptureOptions,
+) -> Option<String> {
+    capture_script(shell_type, options, Replay::Eval)
+}
+
+/// Capture state for incremental sourcing. Parse options and aliases together so
+/// restored aliases and quoting options cannot reinterpret later declarations.
+pub fn snapshot_source_capture_script(
+    shell_type: ShellType,
+    options: SnapshotCaptureOptions,
+) -> Option<String> {
+    capture_script(
+        shell_type,
+        options,
+        if shell_type == ShellType::Sh {
+            Replay::Eval
+        } else {
+            Replay::Source
+        },
+    )
+}
+
+enum Replay {
+    Eval,
+    Source,
+}
+
+fn capture_script(
+    shell_type: ShellType,
+    options: SnapshotCaptureOptions,
+    replay: Replay,
 ) -> Option<String> {
     let script = match shell_type {
         ShellType::Zsh => zsh_snapshot_script(options.startup),
@@ -56,6 +86,8 @@ pub fn snapshot_capture_script(
     };
     Some(
         script
+            .replace("SNAPSHOT_OPTIONS_BEGIN", match replay { Replay::Eval => "", Replay::Source => "printf '{\\n'" })
+            .replace("SNAPSHOT_ALIASES_END", match replay { Replay::Eval => "", Replay::Source => "printf \"case '' in '') ;; esac\\n}\\n\"" })
             .replace("SNAPSHOT_EXPORTS", &declarations)
             .replace(
                 "SNAPSHOT_DECLARATION_ENVIRONMENT",
@@ -92,16 +124,18 @@ print 'unalias -a 2>/dev/null || true'
 print '# Functions'
 functions
 print ''
+SNAPSHOT_OPTIONS_BEGIN
 SNAPSHOT_COMMAND_HELPER
 setopt_count=$(setopt | __codex_snapshot_command wc -l | __codex_snapshot_command tr -d ' ')
 print "# setopts $setopt_count"
 setopt | __codex_snapshot_command sed 's/^/setopt /'
 print ''
 printf '\0'
-alias_count=$(alias -L | __codex_snapshot_command wc -l | __codex_snapshot_command tr -d ' ')
+alias_count=$(\alias -L | __codex_snapshot_command wc -l | __codex_snapshot_command tr -d ' ')
 print "# aliases $alias_count"
-alias -L
+\alias -L
 print ''
+SNAPSHOT_ALIASES_END
 printf '\0'
 SNAPSHOT_EXPORTS
 printf '\0'
@@ -122,6 +156,7 @@ shopt -p || true
 echo '# Functions'
 declare -f
 echo ''
+SNAPSHOT_OPTIONS_BEGIN
 SNAPSHOT_COMMAND_HELPER
 bash_opts=$(set -o | __codex_snapshot_command awk '$2=="on"{print $1}')
 bash_opt_count=$(printf '%s\n' "$bash_opts" | __codex_snapshot_command sed '/^$/d' | __codex_snapshot_command wc -l | __codex_snapshot_command tr -d ' ')
@@ -131,10 +166,11 @@ if [ -n "$bash_opts" ]; then
 fi
 echo ''
 printf '\0'
-alias_count=$(alias -p | __codex_snapshot_command wc -l | __codex_snapshot_command tr -d ' ')
+alias_count=$(\alias -p | __codex_snapshot_command wc -l | __codex_snapshot_command tr -d ' ')
 echo "# aliases $alias_count"
-alias -p
+\alias -p
 echo ''
+SNAPSHOT_ALIASES_END
 printf '\0'
 SNAPSHOT_EXPORTS
 printf '\0'
@@ -180,6 +216,7 @@ elif command -v declare >/dev/null 2>&1; then
   declare -f
 fi
 echo ''
+SNAPSHOT_OPTIONS_BEGIN
 SNAPSHOT_COMMAND_HELPER
 if set -o >/dev/null 2>&1; then
   sh_opts=$(set -o | __codex_snapshot_command awk '$2=="on"{print $1}')
@@ -201,6 +238,7 @@ if alias >/dev/null 2>&1; then
 else
   echo '# aliases 0'
 fi
+SNAPSHOT_ALIASES_END
 printf '\0'
 SNAPSHOT_EXPORTS
 printf '\0'