feat: add BuildRule skill for authoring module rules

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/).
 
 ### Added
 
+- `skills/BuildRule/` — authoring, placement, and validation conventions for behavioral rules (one file one behavior, PascalCase naming, owning-module routing, qualifier directories, token-cost discipline), completing the Build* family
 - `skills/GuardRails/DestructiveCommandGuard.md` companion (dcg block anatomy and workarounds), `skills/IncrementalEdits/` (revise files as reviewable hunks), `skills/SessionSearch/LocalCheckpoints.md`; updates to SettingsMaintenance, SystemCheck, Wtf, ProvenanceAudit, and the ProvenanceAuditor agent
 - `skills/InitProject/` — `project` / `atlas` shell functions that scaffold a workshop project spine (git + jj colocate + entire + forge hooks, private/public/assets flow, `.tlp` manifest, vault-mounted `.claude/`) with on-demand satellites (vault folder-note, `~/Data` domain-path mirror granted to agent sessions, private remote). Config in `~/.config/forge/project.yaml` with `FORGE_*` per-shell overrides; `project init` renders `CLAUDE.md.tmpl` into each project's brief
 - `.githooks/` gains `commit-msg`, `prepare-commit-msg`, `post-commit`, `post-rewrite`, and the pre-entire `pre-push` variant, completing the commit-gate set that `make install` wires via `core.hooksPath`; `BACKLOG.md` tracks module-level follow-ups

skills/BuildRule/SKILL.md

@@ -0,0 +1,53 @@
+---
+name: BuildRule
+version: 0.1.0
+description: "Create, validate, or place behavioral rules in forge modules. USE WHEN create rule, new rule, write rule, capture rule, add a rule, graduate a correction or convention to a rule, validate rule, rule conventions, where does this rule belong, or the user runs /Rule."
+---
+
+# BuildRule
+
+Author, place, and validate the small always-in-context instruction files that steer every session. A rule is the durable form of a correction: when the user says "always do X" or "never do Y again", it becomes a rule, not a memory.
+
+## Rule Conventions
+
+### Shape
+
+A rule is a single `.md` file in the owning module's `rules/` directory. One file, one behavior — when something goes wrong, the filename names the rule that caused it. The only valid subdirectories are locale (`rules/cs-CZ/`), harness and model qualifiers (`rules/claude/`, `rules/claude/claude-opus-4-6/`), and gitignored `user/` overrides; resolution precedence is in PROV-0005.
+
+### Naming
+
+PascalCase, scope + focus, self-explanatory in English: `PreferTrash`, `VerifyClaims`, `NoEmDash`. No spaces, hyphens, or opaque acronyms. The filename is the rule's identity in every error report.
+
+### Frontmatter
+
+Optional. When present: `name`, `version`, `description`, `targets` (harness filter), `mode` (`replace` | `append` | `prepend`, qualifier variants only). Assembly strips frontmatter at deploy — never put load-bearing content there.
+
+### Body
+
+Concise, actionable prose stating the current truth (PresentTense; no backstory). A wrong/right example pair beats three paragraphs of explanation. No headings needed; max depth 3 if used. Cite sources for factual claims (CiteSources).
+
+**Every word costs tokens on every interaction** — rules are always in context. If the model already does it unprompted, the rule belongs in a model qualifier directory or nowhere (see OptimizeContext). If it needs more than ~20 lines, it is probably a skill, not a rule.
+
+### Placement
+
+Rules are authored in the owning module's `rules/`, never directly in `~/.claude/` (AuthorInModules — deployed files get overwritten on install). Route by subject: version-control behavior → the module owning VersionControl; vault conventions → forge-obsidian; no clear owner → forge-steering. Prefer folding a new constraint into an existing rule on the same subject over creating a near-duplicate file (LessIsMore).
+
+## Create Workflow
+
+1. **Distill the behavior** — one sentence stating what must (or must never) happen, generalized beyond the incident that prompted it. Include the why only when the rule is not self-evident.
+2. **Find the owner** — `grep -l <topic> */rules/*.md` across modules; extend an existing rule if one covers the subject.
+3. **Write the file** following the conventions above.
+4. **Deploy** — `make install` from the module (or mirror the edit into the deployed `~/.claude/rules/` copy for immediate effect in the current session).
+5. **Land it** — commit in the module repo per its VCS flow; rules ride normal PRs.
+
+## Validate Workflow
+
+- [ ] Single `.md` file in `rules/` (or a valid qualifier subdirectory)
+- [ ] PascalCase filename naming the behavior
+- [ ] One behavior; no bundled unrelated constraints
+- [ ] Body is present-tense instruction, no narration of what changed
+- [ ] Short enough to justify its permanent token cost
+- [ ] Not a duplicate — no existing rule covers the same subject
+- [ ] Factual claims carry sources
+
+Report **COMPLIANT** or **NON-COMPLIANT** with specific fixes.