fix(writing-skills): correct false 'only two fields' frontmatter claim (#882)

8 tasks covering: environment detection in using-git-worktrees,
Step 1.5 + cleanup guard in finishing-a-development-branch,
Integration line updates, codex-tools.md docs, automated tests,
and final verification.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

skills/writing-skills/SKILL.md

@@ -93,7 +93,7 @@ skills/
 ## SKILL.md Structure
 
 **Frontmatter (YAML):**
-- Only two fields supported: `name` and `description`
+- Two required fields: `name` and `description` (see [agentskills.io/specification](https://agentskills.io/specification) for all supported fields)
 - Max 1024 characters total
 - `name`: Use letters, numbers, and hyphens only (no parentheses, special chars)
 - `description`: Third-person, describes ONLY when to use (NOT what it does)
@@ -604,7 +604,7 @@ Deploying untested skills = deploying untested code. It's a violation of quality
 
 **GREEN Phase - Write Minimal Skill:**
 - [ ] Name uses only letters, numbers, hyphens (no parentheses/special chars)
-- [ ] YAML frontmatter with only name and description (max 1024 chars)
+- [ ] YAML frontmatter with required `name` and `description` fields (max 1024 chars; see [spec](https://agentskills.io/specification))
 - [ ] Description starts with "Use when..." and includes specific triggers/symptoms
 - [ ] Description written in third person
 - [ ] Keywords throughout for search (errors, symptoms, tools)

skills/writing-skills/anthropic-best-practices.md

@@ -144,7 +144,7 @@ What works perfectly for Opus might need more detail for Haiku. If you plan to u
 ## Skill structure
 
 <Note>
-  **YAML Frontmatter**: The SKILL.md frontmatter supports two fields:
+  **YAML Frontmatter**: The SKILL.md frontmatter requires two fields:
 
   * `name` - Human-readable name of the Skill (64 characters maximum)
   * `description` - One-line description of what the Skill does and when to use it (1024 characters maximum)
@@ -1092,7 +1092,7 @@ reader = PdfReader("file.pdf")
 
 ### YAML frontmatter requirements
 
-The SKILL.md frontmatter includes only `name` (64 characters max) and `description` (1024 characters max) fields. See the [Skills overview](/en/docs/agents-and-tools/agent-skills/overview#skill-structure) for complete structure details.
+The SKILL.md frontmatter requires `name` (64 characters max) and `description` (1024 characters max) fields. See the [Skills overview](/en/docs/agents-and-tools/agent-skills/overview#skill-structure) for complete structure details.
 
 ### Token budgets