#595 Emit complete YAML frontmatter from resolve-frontmatter.sh

[williamthorsen]

What

Skills and subagents authoring artifacts no longer compose YAML frontmatter by hand: resolve-frontmatter.sh now emits the complete frontmatter, which callers prepend verbatim. The _partials/frontmatter-via-script.md partial is removed. Existing --format json callers are unchanged.

Why

Before this change, every skill and subagent's frontmatter resolution section had the agent compose YAML by hand from the script's JSON output: Parse the JSON, map fields to YAML keys, enforce omission rules, lay out the correct field order, and quote values correctly. This was a non-trivial composition surface duplicated across ~24 sites. Schema changes required coordinated prose updates everywhere, and there was room for subtle mis-formatting (pr: null instead of omission; field reordering; mis-quoted ticket_ref: '#537'). Moving composition into the script makes the schema single-sourced — field order, quoting, omission, and per-section grouping are all the script's responsibility, owned and tested in one place.

Details

♻️ Refactoring

• Twelve skills and ten subagents converted from <!-- include: ../../_partials/frontmatter-via-script.md --> + per-skill bullets to a single Bash invocation sentence. Each site passes its --skill, --interactive, and (where applicable) --model flags inline; extension fields previously documented as bullets now appear as --extra / --extra-list flags on the invocation line.
• create-devlog and summarize-change use bash conditional expansion (${var:+--flag "key=$var"}) for optional fields so the snippets are self-evidently correct when values are empty, rather than relying on the script's omission behavior to suppress empty extras.
• The obsolete _partials/frontmatter-via-script.md partial was deleted.
• Inline YAML frontmatter examples in 13 ## Output format sections were replaced with a sentence referencing the canonical example in _data/artifact-conventions.md. Subagent-tier files use bare prose references (their install pipeline does not rewrite paths); skill-tier files use Markdown links.
• A new ### Bespoke frontmatter composition subsection in _data/artifact-conventions.md documents the two sites that opt into --format json and the structural reason each one does.

🐛 Bug fixes

• The YAML emission path now omits scalar extension fields whose resolved value is empty, matching the documented omission rule for canonical fields and the script's header documentation.
• emit_yaml_flow_list disables shell globbing around its word-split, preventing list values that contain glob characters (*, ?, [...]) from being silently expanded against the filesystem.
• Passing a duplicate --extra or --extra-list key now surfaces a stderr warning before overwriting; the previous behavior was silent overwrite.

🧪 Tests

• Test coverage grew from 217 to 282 shellspec examples.
• New tests cover the auto-quoting predicate across YAML-special characters (#, :, leading sigils - / ? / :, embedded single quotes, brackets, braces, empty values, and nine additional glyphs), extension insertion order across mixed --extra and --extra-list, single-element flow lists, and --override KEY= force-omit semantics.
• New end-to-end integration tests drive main() directly with stubbed git and gh, covering required-arg validation (missing --skill, missing --interactive, unknown --format), and the full flag-to-output wiring path.
• A snapshot test pins --format json byte-equivalence so future schema changes cannot silently break existing JSON callers.

📚 Docs

• The shared PR-resolution contract document (pr-resolution.md) was de-staled to match the new default output format — prose previously referred to "JSON output" in three places where the contract is actually format-agnostic.

Closes #595

[github-actions]

Dependency audit

Production dependency audit passed.