docs: add branch naming convention to AGENTS.md and CONTRIBUTING.md (#2678)

- AGENTS.md: branch naming as a requirement for AI coding agents
- CONTRIBUTING.md: branch naming as a recommendation for human contributors
- Convention: <type>/<number>-<short-slug> where number is issue or PR number

Closes #2677

Author: mnriem

AGENTS.md

@@ -379,6 +379,32 @@ Implementation: Extends `YamlIntegration` (parallel to `TomlIntegration`):
 4. Uses `yaml.safe_dump()` for header fields to ensure proper escaping
 5. Sets `context_file = "AGENTS.md"` so the base setup manages the Spec Kit context section there
 
+## Branch Naming Convention
+
+All branches **must** follow this pattern:
+
+```
+<type>/<number>-<short-slug>
+```
+
+Where `<number>` is either an issue number or a PR number — whichever is created first.
+
+| Prefix | When to use | Example |
+|---|---|---|
+| `feat/` | New features | `feat/2342-workflow-cli-alignment` |
+| `fix/` | Bug fixes | `fix/2653-paths-only-validation` |
+| `docs/` | Documentation changes | `docs/2677-branch-naming-convention` |
+| `community/` | Community catalog additions | `community/2492-add-mde-extension` |
+| `chore/` | Maintenance, tooling, CI | `chore/2366-editorconfig` |
+
+**Rules:**
+
+1. Always include the issue or PR number immediately after the prefix — this is what makes branches traceable
+2. Use kebab-case for the slug
+3. Keep the slug short — enough to identify the work without looking up the issue
+
+---
+
 ## Common Pitfalls
 
 1. **Using shorthand keys for CLI-based integrations**: For CLI-based integrations (`requires_cli: True`), the `key` must match the executable name (e.g., `"cursor-agent"` not `"cursor"`). `shutil.which(key)` is used for CLI tool checks — mismatches require special-case mappings. IDE-based integrations (`requires_cli: False`) are not subject to this constraint.

CONTRIBUTING.md

@@ -38,7 +38,7 @@ On [GitHub Codespaces](https://github.com/features/codespaces) it's even simpler
 1. Fork and clone the repository
 1. Configure and install the dependencies: `uv sync --extra test`
 1. Make sure the CLI works on your machine: `uv run specify --help`
-1. Create a new branch: `git checkout -b my-branch-name`
+1. Create a new branch: `git checkout -b <type>/<number>-<short-slug>` (see [Branch naming](#branch-naming) below)
 1. Make your change, add tests, and make sure everything still works
 1. Test the CLI functionality with a sample project if relevant
 1. Push to your fork and submit a pull request
@@ -55,6 +55,20 @@ Here are a few things you can do that will increase the likelihood of your pull
 - Write a [good commit message](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html).
 - Test your changes with the Spec-Driven Development workflow to ensure compatibility.
 
+### Branch naming
+
+We recommend naming branches as `<type>/<number>-<short-slug>`, where `<number>` is the issue or PR number (whichever comes first) and `<type>` is one of:
+
+| Prefix | When to use | Example |
+|---|---|---|
+| `feat/` | New features | `feat/2342-workflow-cli-alignment` |
+| `fix/` | Bug fixes | `fix/2653-paths-only-validation` |
+| `docs/` | Documentation changes | `docs/2677-branch-naming-convention` |
+| `community/` | Community catalog additions | `community/2492-add-mde-extension` |
+| `chore/` | Maintenance, tooling, CI | `chore/2366-editorconfig` |
+
+Including the issue or PR number makes branches traceable — especially useful since the project uses squash merges and `git branch --merged` won't detect merged branches. If you start with a PR (no issue), use the PR number once it's assigned.
+
 ## Development workflow
 
 When working on spec-kit: