metrics_compare_base: catch TimeoutExpired; fix code-size skill docs

- run() now catches subprocess.TimeoutExpired (only triggered by `cmake --build`'s
  timeout=600) and returns CompletedProcess(rc=124) so the caller falls through to
  error reporting and worktree cleanup instead of crashing with a traceback.
- code-size SKILL.md: document the actual default filter (per-side absolute
  <checkout>/src/ path, not the old `tinyusb/src` substring) and adjust the
  reporting guidance to match what the report rows actually contain.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

1 files changed, 10 insertions, 2 deletions

diff --git a/tools/metrics_compare_base.py b/tools/metrics_compare_base.py
index 0fb767bb7..a541dae79 100644
--- a/tools/metrics_compare_base.py
+++ b/tools/metrics_compare_base.py
@@ -37,12 +37,20 @@ verbose = False
 
 
 def run(cmd, **kwargs):
-    """Run a command. cmd must be a list (no shell=True)."""
+    """Run a command. cmd must be a list (no shell=True). On `timeout=`-induced
+    TimeoutExpired, return a CompletedProcess with rc=124 instead of letting the
+    exception propagate, so the caller can fall through to error reporting and
+    worktree cleanup rather than crashing with a traceback."""
     if not isinstance(cmd, list):
         raise TypeError('run() requires a list, got str — fix the caller')
     if verbose:
         print(f'  $ {" ".join(shlex.quote(str(c)) for c in cmd)}')
-    return subprocess.run(cmd, capture_output=True, text=True, **kwargs)
+    try:
+        return subprocess.run(cmd, capture_output=True, text=True, **kwargs)
+    except subprocess.TimeoutExpired as e:
+        msg = f'Command timed out after {e.timeout}s: {" ".join(shlex.quote(str(c)) for c in cmd)}'
+        stderr = (e.stderr or '') + ('\n' if e.stderr else '') + msg
+        return subprocess.CompletedProcess(cmd, 124, stdout=(e.stdout or ''), stderr=stderr)
 
 
 def symlink_deps(main_root, worktree_dir):