chore: add shared agent project configuration

.claude/skills/trellis-before-dev/SKILL.md

@@ -0,0 +1,55 @@
+---
+name: trellis-before-dev
+description: 'Discovers and injects project-specific coding guidelines from .trellis/spec/ before implementation begins. Reads spec indexes, pre-development checklists, and shared thinking guides for the target package. Use when starting a new coding task, before writing any code, switching to a different package, or needing to refresh project conventions and standards.'
+---
+
+Read the relevant development guidelines before starting your task.
+
+Execute these steps:
+
+1. **Read current task artifacts**:
+   - `prd.md` for requirements and acceptance criteria
+   - `design.md` if present for technical design
+   - `implement.md` if present for execution order and validation plan
+
+2. **Discover packages and their spec layers**:
+
+   ```bash
+   python3 ./.trellis/scripts/get_context.py --mode packages
+   ```
+
+3. **Identify which specs apply** to your task based on:
+   - Which package you're modifying (e.g., `cli/`, `docs-site/`)
+   - What type of work (backend, frontend, unit-test, docs, etc.)
+   - Any spec/research paths referenced by the task artifacts
+
+4. **Read the spec index** for each relevant module:
+
+   ```bash
+   cat .trellis/spec/<package>/<layer>/index.md
+   ```
+
+   Follow the **"Pre-Development Checklist"** section in the index.
+
+5. **Read the specific guideline files** listed in the Pre-Development Checklist that are relevant to your task. The index is NOT the goal — it points you to the actual guideline files (e.g., `error-handling.md`, `conventions.md`, `mock-strategies.md`). Read those files to understand the coding standards and patterns.
+
+6. **Always read shared guides**:
+
+   ```bash
+   cat .trellis/spec/guides/index.md
+   ```
+
+7. **For a non-trivial task, state the change boundary before writing code.** Non-trivial means it touches more than one file, crosses a layer, changes a public interface, or edits code you did not just write. Write down:
+   - the smallest behavior gap between what happens now and what should happen
+   - where that behavior actually lives (not where it is easiest to intercept)
+   - which files you expect to change, and why each one is necessary
+   - what you are explicitly not doing in this task
+   - if a local refactor is needed, how you will show it did not change behavior
+
+   A small, well-scoped change does not need this — do it directly.
+
+   If the real scope turns out to be clearly larger than this, say so and why before continuing. Do not widen the change on your own.
+
+8. Understand the coding standards and patterns you need to follow, then proceed with your development plan.
+
+This step is **mandatory** before writing any code.