Fix entrypoint lookup in package debug-symbol smoke tests (#56032)

## Why

Rust v0 symbols can mention `codex_code_mode_host` as the instantiating crate of a dependency's generic function, so matching the crate name alone can select the wrong function.

## What changed

Demangle `nm` output and match `codex_code_mode_host::main` exactly, preserving spaces within demangled names. Include local symbols in the Linux lookup by removing `--extern-only`.

GitOrigin-RevId: b4ea4face3fe861966d3643d13db168143bcefa3

scripts/codex_package/smoke_tests/test_codex_package.py

@@ -161,7 +161,7 @@ def _code_mode_host_symbol_address(
     *arguments: str,
 ) -> str:
     symbol_output = subprocess.run(
-        ["nm", *arguments, str(symbols)],
+        ["nm", "-C", *arguments, str(symbols)],
         cwd=package.directory,
         env=package.environment,
         capture_output=True,
@@ -169,12 +169,14 @@ def _code_mode_host_symbol_address(
         check=True,
         timeout=45,
     ).stdout
+    # Rust v0 symbols can name this crate only as the instantiating crate of
+    # a dependency's generic function. Match the demangled entrypoint instead.
     return next(
         parts[0]
         for line in symbol_output.splitlines()
-        if len(parts := line.split()) == 3
+        if len(parts := line.split(maxsplit=2)) == 3
         and parts[1].lower() == "t"
-        and "codex_code_mode_host" in parts[2]
+        and parts[2] == "codex_code_mode_host::main"
     )
 
 
@@ -185,7 +187,7 @@ def test_linux_debug_symbols_resolve_packaged_code(
 ) -> None:
     """Linux host symbols resolve a packaged function and its source location."""
     address = _code_mode_host_symbol_address(
-        package, code_mode_host_debug_symbols, "--defined-only", "--extern-only"
+        package, code_mode_host_debug_symbols, "--defined-only"
     )
     resolved = subprocess.run(
         [