Preserve zsh tied PATH exports in shell snapshots (#34293)

## Why

zsh prints tied scalar/array exports such as `PATH` and `path` with `-T`
metadata. The snapshot filter rejected that syntax, so commands available only
through the configured `PATH` could not be resolved from a restored snapshot.

## What changed

- Recognize writable tied exports and retain them in zsh shell snapshots.
- Skip readonly exports so restoring a snapshot does not make variables such as
  `PATH` immutable.

## Testing

Added macOS coverage for restoring a tied `PATH`, handling entries with spaces,
deduplicating path entries, excluding readonly tied exports, and resolving a
command available only through the restored snapshot.

GitOrigin-RevId: 297cfae3368230c7f6fe5ef84f0a10b35a2c802c

codex-rs/core/src/shell_snapshot.rs

@@ -342,6 +342,13 @@ export_lines=$(export -p | awk '
   line=$0
   name=line
   sub(/^(export|declare -x|typeset -x) /, "", name)
+  if (name ~ /^-[A-Za-z]*r[A-Za-z]* /) {
+    next
+  }
+  if (name ~ /^-[A-Za-z]*T[A-Za-z]* /) {
+    sub(/^-[A-Za-z]*T[A-Za-z]* /, "", name)
+    sub(/ [A-Za-z_][A-Za-z0-9_]*=.*/, "", name)
+  }
   sub(/=.*/, "", name)
   if (name ~ /^(EXCLUDED_EXPORTS)$/) {
     next