fix(core): frontmatter keys are read at top level only, never from nested maps

[Max17190]

Why

Round-7 contract audit, the round's one P2, reproduced on a built binary. parse_skill_source and the shared frontmatter_descriptions reader matched name:/description: on TRIMMED lines, last wins, at any depth. The standard skill frontmatter commonly carries a metadata: block; a field of it spelled name: or description: silently stole the skill's identity:

---
name: pdf-tools
description: Extract text and tables from PDF files.
metadata:
  name: internal-scratch
  description: not for the index
---

loaded as skill 'internal-scratch' with description not for the index, the frozen index carried the stolen strings, the #250 portability warning evaluated a name the author never wrote, and --check reported ok. It was the only state found where the verification surface certifies a broken outcome. A description: block scalar containing a line that starts with name: hit the same path, because the name loop had no block-scalar awareness.

Summary

• Both readers match keys only at the block's top level (no leading indentation). That single rule also excludes block-scalar content, whose lines are always indented past their key, so the name loop needs no scalar tracking.
• Templates share frontmatter_descriptions, so a description: nested under metadata: in a prompt template no longer becomes the popup line.
• --spec skills states the top-level rule, so the text and the binary agree.
• Top-level last-wins semantics for SKILL.md and first-wins for templates are unchanged (fix(skills): read block scalar descriptions instead of indexing the > header #227).

Test Plan

• a_nested_frontmatter_key_does_not_override_the_skill_name: the reproduction above; asserts the top-level name and description survive. Red on the old readers.
• a_block_scalar_line_spelling_name_does_not_become_the_name: a description: > scalar containing name: ... prose; asserts the name is untouched and the folded description keeps the line. Red on the old readers.
• a_nested_description_is_not_the_template_description (templates): a nested-only description leaves the popup line empty. Red on the old readers.
• Full workspace suite green (exit 0), clippy at zero warnings.

Greptile Summary

This change limits skill and prompt-template frontmatter metadata to unindented top-level keys. Nested map fields and block-scalar prose can no longer replace the displayed skill name or description.

Runtime checks exercised real skill discovery, template discovery, and template invocation. They confirmed that valid top-level metadata remains available, nested keys are ignored, and valid top-level keys appearing after nested or scalar content are still read. The same harness demonstrated the prior nested-template-description behavior on the parent revision and passed on this revision.

No defects were found.

Confidence Score: 5/5

The metadata parsing change is safe to merge based on exercised discovery and invocation behavior.

The affected behavior was checked with real skill and template fixtures, including nested maps, block-scalar content resembling metadata, nested-only template descriptions, and later valid top-level keys. The current implementation produced the intended results.

Files Needing Attention: No files need follow-up attention.

T-Rex Logs

What T-Rex did

• Before PR fix(core): frontmatter keys are read at top level only, never from nested maps #255, the harness returned a nested template description instead of the actual skill description, causing the harness assertion to fail with exit code 101.
• After applying the current checkout, the harness shows the skill name as actual-later-name, the skill description as actual later skill description, the nested-only template description is empty, and template expansion succeeds with exit code 0.
• Targeted unit tests for the three PR fix(core): frontmatter keys are read at top level only, never from nested maps #255 cases were executed and passed under the new validation.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "fix(core): frontmatter keys are read at ..." | Re-trigger Greptile}