chore: restructure agent skills/rules and add Codex support

.claude/skills/dep-upgrade/instructions.md → .agents/skills/dep-upgrade/instructions.md

@@ -2,8 +2,7 @@
 
 ## 1. Breaking Changes Analysis
 
-Fetch the official migration guide via WebFetch. For each breaking change, grep `src/`, config files,
-and `package.json` to determine applicability. Produce two tables:
+Fetch the official migration guide via WebFetch. For each breaking change, grep `src/`, config files, and `package.json` to determine applicability. Produce two tables:
 
 **問題なし（対応不要）**
 
@@ -26,14 +25,12 @@ Key areas to check:
 
 ## 2. Companion Package Check
 
-Some packages must be upgraded together in the same commit to avoid version mismatch.
-Check `package.json` for known companion pairs:
+Some packages must be upgraded together in the same commit to avoid version mismatch. Check `package.json` for known companion pairs:
 
 - `@sveltejs/kit` + `@sveltejs/vite-plugin-svelte`
 - `eslint` + `@eslint/js`
 
-Also verify peer dependency compatibility (`"eslint": "^8 || ^9 || ^10"` style) for all
-related packages already installed.
+Also verify peer dependency compatibility (`"eslint": "^8 || ^9 || ^10"` style) for all related packages already installed.
 
 If companion packages are found, include them in the upgrade scope.
 
@@ -66,9 +63,6 @@ pnpm check
 pnpm test:unit
 ```
 
-> **`pnpm check` tip:** If type errors appear and you have uncommitted changes, run
-> `git stash && pnpm check 2>&1 | tail -5` to confirm whether errors are pre-existing.
-> Restore with `git stash pop`. If there is nothing to stash, skip this check — without
-> a baseline to compare against, it gives no useful signal.
+> **`pnpm check` tip:** If type errors appear and you have uncommitted changes, run `git stash && pnpm check 2>&1 | tail -5` to confirm whether errors are pre-existing. Restore with `git stash pop`. If there is nothing to stash, skip this check — without a baseline to compare against, it gives no useful signal.
 
 Update the plan.md `- [ ]` checklist and add a verification results table when done.

.agents/skills/extract-approach/SKILL.md

@@ -0,0 +1,14 @@
+---
+name: extract-approach
+description: Use when a non-trivial problem has just been solved (bug fixed after debugging, tricky implementation completed, blocker resolved) and the session is about to move on. A solution without its learnings note is unfinished work.
+argument-hint: '[task-name-en]'
+---
+
+Extract the approach from the just-solved problem into a learnings note for: $ARGUMENTS
+
+**Skip when:** trivial fixes (typo, rename, config tweak), dependency bumps, or the insight is already covered by `docs/guides/agent-rules/` or the task's `plan.md`.
+
+1. **Identify the problem** — the symptom from this session and what made it non-trivial; multiple candidates → confirm which one with AskUserQuestion
+2. **Extract** — 問題 / 有効だったアプローチ / ハマった点 / 教訓 only; apply the extraction and abstraction rules in [instructions.md](instructions.md)
+3. **Write the note** — `docs/dev-notes/YYYY-MM-DD/{task-name-en}/learning.md`; naming and format rules in [instructions.md](instructions.md)
+4. **Escalate durable rules** — propose target file and exact wording for project-wide conventions; **do not apply without user confirmation**

.agents/skills/extract-approach/instructions.md

@@ -0,0 +1,34 @@
+# extract-approach instructions
+
+## What to extract
+
+Record only what changes future behavior. No session log, no timestamps, no narration of the order things happened in.
+
+| Section              | Content                                       |
+| -------------------- | --------------------------------------------- |
+| 問題                 | Symptom and root cause, one line each         |
+| 有効だったアプローチ | What worked, and **why** it worked            |
+| ハマった点           | Dead ends actually tried, and why each failed |
+| 教訓                 | Reusable rules that apply beyond this task    |
+
+Omit a section that has nothing real to say. An empty ハマった点 is a signal the problem may have been trivial — reconsider the skip condition.
+
+## Align abstraction (抽象度を揃える)
+
+State every 教訓 at the same level of generality:
+
+- One general rule per bullet, optionally followed by a single concrete example from this session.
+- Never mix operational steps and principles in the same list.
+- A bullet that only makes sense for this one file or this one bug is not a 教訓 — move it to 有効だったアプローチ or drop it.
+
+## Note format
+
+- Path: `docs/dev-notes/YYYY-MM-DD/{task-name-en}/learning.md`, using today's date.
+- Directory name: `$ARGUMENTS` if given; else the `plan.md` directory name of the task this problem belongs to (when the session is executing one); else a short kebab-case name.
+- Japanese prose, English code identifiers, 30 lines or fewer.
+- One semantic paragraph or list item per line; no width-based hard line breaks.
+- If the file already exists, append a `---`-separated entry instead of rewriting it.
+
+## Escalating to a durable rule
+
+A 教訓 belongs in a rules document when it would apply to an unrelated future task in the same path. Propose the target file under `docs/guides/agent-rules/` (or `AGENTS.md` for a project-wide principle) and the exact wording, then wait for the user's decision.

.claude/skills/verify-test-strength/instructions.md → .agents/skills/verify-test-strength/instructions.md

@@ -36,4 +36,4 @@ Read stdout from `--reporter=default` / `--reporter=verbose`. **Never read a cac
 - **A test catching nothing that other tests miss** — a deletion candidate. Confirm by re-running the full mutant set without it.
 - **N tests failing on one mutant** — not N times the value. Parameterized cases over one fixture usually report the same fact N times; the count is a proxy, not evidence.
 
-Record the matrix in the commit message or `plan.md` when it justifies removing tests — it is the evidence `.claude/rules/testing.md` requires for a deliberate test-count drop.
+Record the matrix in the commit message or `plan.md` when it justifies removing tests — it is the evidence `docs/guides/agent-rules/testing.md` requires for a deliberate test-count drop.

.claude/rules/accessibility.md

@@ -0,0 +1 @@
+../../docs/guides/agent-rules/accessibility.md

.claude/rules/auth.md

@@ -0,0 +1 @@
+../../docs/guides/agent-rules/auth.md

.claude/rules/coding-style.md

@@ -0,0 +1 @@
+../../docs/guides/agent-rules/coding-style.md

.claude/rules/github-actions.md

@@ -0,0 +1 @@
+../../docs/guides/agent-rules/github-actions.md