feat: add agent skills for agentic SDLC

.agents/skills/code-review/SKILL.md

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+---
+name: code-review
+description: >-
+  Review a pull request or code change in tekton-pruner. Use when asked to
+  review a PR, evaluate a diff, or assess code quality. Applies Tekton community
+  standards, Go best practices, operator patterns, and pruner-specific domain
+  knowledge (reconciler logic, ConfigMap validation, TTL/history semantics).
+license: Apache-2.0
+metadata:
+  project: tekton-pruner
+allowed-tools: Read Grep Glob Bash(git diff:*) Bash(git log:*)
+---
+
+# Code Review
+
+tekton-pruner follows [Tekton community review standards](https://github.com/tektoncd/community/blob/main/standards.md).
+
+## Review Checklist
+
+### Correctness
+
+- [ ] Logic changes have corresponding unit tests in the relevant `_test.go` file
+- [ ] New ConfigMap fields are covered in `pkg/config/config_validation_test.go`
+  and `config_validation_hierarchical_test.go`
+- [ ] Reconciler changes do not break idempotency (re-running reconcile must be safe)
+- [ ] TTL and history-limit logic in `pkg/config/ttl_handler.go` and
+  `history_limiter.go` correctly handles zero-value, negative, and missing fields
+- [ ] No data races — verify with `make test-unit` (race detector is on by default)
+
+### Go Quality
+
+- [ ] `make fmt` produces no diff
+- [ ] `go vet ./...` is clean
+- [ ] No use of `init()` for non-trivial side effects
+- [ ] Errors are wrapped with `fmt.Errorf("...: %w", err)` — not swallowed
+- [ ] Contexts are propagated, not ignored
+- [ ] No direct use of `os.Exit` outside `main`
+
+### Kubernetes / Operator Patterns
+
+- [ ] RBAC changes in `config/200-clusterrole.yaml` / `config/200-role.yaml`
+  are least-privilege — add only the verbs actually required
+- [ ] New CRDs or config resources include corresponding YAML in `config/`
+- [ ] Informers and listers are used for reads; direct API calls for writes
+- [ ] Reconcile loops return `controller.NewPermanentError` only for truly
+  unrecoverable conditions
+- [ ] Webhook validation in `pkg/webhook/configmapvalidation.go` rejects invalid
+  pruner specs early, with clear error messages
+
+### Domain: Pruner Logic
+
+- [ ] ConfigMap selector logic (`pkg/config/config.go`, `pkg/config/helper.go`) correctly
+  resolves namespace-level overrides vs cluster-level defaults
+- [ ] `pkg/config/constants.go` is the single source of truth for annotation
+  and label keys — no hardcoded strings elsewhere
+- [ ] History and TTL limits are validated against each other where both are set
+- [ ] The pruner reconciler correctly handles `PipelineRun` and `TaskRun`
+  independently; shared logic belongs in `pkg/config/helper.go`
+
+### Observability
+
+- [ ] New controller actions emit metrics via `pkg/metrics/`
+- [ ] Log statements use structured logging (`zap`) with appropriate levels
+  (`Info` for normal operations, `Error` for failures, `Debug` for verbose paths)
+
+### Documentation
+
+- [ ] Public functions and types have Go doc comments
+- [ ] User-facing ConfigMap fields are documented in `docs/` (especially
+  `docs/tutorials/` and `docs/configmap-validation.md`)
+- [ ] `ARCHITECTURE.md` is updated if a new component or major design change
+  is introduced
+
+## What to Approve
+
+Approve when:
+- All checklist items pass
+- Tests cover the changed behavior
+- The change is focused (one concern per PR)
+- Commit messages follow [Tekton commit conventions](https://github.com/tektoncd/community/blob/main/standards.md#commit-messages)
+
+## What to Block
+
+Block (request changes) when:
+- Logic is untested or tests are trivially green
+- RBAC grants broad wildcard verbs
+- Errors are silently swallowed in reconcile loops
+- ConfigMap validation can be bypassed

.agents/skills/commit-message/SKILL.md

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+---
+name: commit-message
+description: >-
+  Generate a conventional commit message for tekton-pruner. Use when the user
+  asks to "create a commit", "generate commit message", "commit changes",
+  "make a commit", mentions "conventional commits", or discusses commit message
+  formatting. Provides guided workflow for creating properly formatted commit
+  messages with line length validation and required trailers.
+version: 0.1.0
+license: Apache-2.0
+metadata:
+  project: tekton-pruner
+allowed-tools: Bash(git diff:*) Bash(git status:*) Bash(git log:*) Bash(git config:*) Read
+---
+
+# Conventional Commit Message Creation
+
+Create properly formatted conventional commit messages following
+project standards with line length validation and required trailers.
+
+## Purpose
+
+Generate commit messages that:
+
+- Follow conventional commits format (`type(scope): description`)
+- Use component names from changed file paths as scope
+- Respect line length limits (50 for subject, 72 for body)
+- Include required trailers (`Signed-off-by`, `Assisted-by`)
+- Follow [Tekton commit conventions](https://github.com/tektoncd/community/blob/main/standards.md#commit-messages)
+  (imperative mood, line length limits; conventional commit prefixes
+  are project practice, not in the written standard)
+
+## Quick Workflow
+
+1. Analyze changes: `git status` and `git diff --cached`
+2. Determine type and scope (see tables below)
+3. Generate message with proper format
+4. Add required trailers
+5. **Never commit without explicit user confirmation**
+
+## Format
+
+```
+<type>(<scope>): <description>
+
+<optional body — explain what and why, not how>
+
+<trailers>
+```
+
+## Type Selection
+
+| Type | When to use |
+|------|-------------|
+| `feat` | New functionality |
+| `fix` | Bug fix |
+| `docs` | Documentation only |
+| `refactor` | Code restructure, no behavior change |
+| `test` | Adding or updating tests |
+| `chore` | Maintenance, dependency updates |
+| `build` | Build system or tooling changes |
+| `ci` | CI/CD workflow changes |
+| `perf` | Performance improvement |
+| `style` | Formatting, linting fixes |
+| `revert` | Reverting a previous commit |
+
+See `references/commit-types.md` for detailed examples.
+
+## Scope Rules
+
+Derive scope from the changed file paths:
+
+| Path pattern | Scope |
+|-------------|-------|
+| `pkg/reconciler/pipelinerun/` | `pipelinerun` |
+| `pkg/reconciler/taskrun/` | `taskrun` |
+| `pkg/reconciler/tektonpruner/` | `controller` |
+| `pkg/reconciler/namespaceprunerconfig/` | `controller` |
+| `pkg/config/` | `config` |
+| `pkg/webhook/` | `webhook` |
+| `pkg/metrics/` | `metrics` |
+| `cmd/controller/` | `controller` |
+| `cmd/webhook/` | `webhook` |
+| `config/` | `config` |
+| `docs/` | scope = doc topic |
+| `.github/workflows/` | `.github/workflows` |
+| `.tekton/` | `.tekton` |
+| `Makefile` | `Makefile` |
+| `go.mod` / `go.sum` / `vendor/` | `deps` |
+| `hack/` | `hack` |
+| `skills/` | `skills` |
+
+If changes span multiple scopes, use the most significant one.
+To link work to a GitHub issue, add `Fixes #NNN` or `Closes #NNN`
+in the commit body (not the subject scope).
+
+## Line Length
+
+- **Subject**: target 50 characters, hard limit 72
+- **Body**: wrap at 72 characters per line
+
+## Required Trailers
+
+Every commit must include:
+
+1. **`Signed-off-by`** — for DCO compliance
+
+   Detection priority:
+   - `$GIT_AUTHOR_NAME` / `$GIT_AUTHOR_EMAIL` environment variables
+   - `git config user.name` / `git config user.email`
+   - Ask user (last resort)
+
+2. **`Assisted-by`** — when AI assists with the commit
+
+   Format: `Assisted-by: <Model Name> (via <Tool Name>)`
+
+   **Do not use `Co-Authored-By` for AI attribution.** The Tekton
+   community adopted `Assisted-by` to distinguish AI assistance from
+   human co-authorship. `Co-Authored-By` implies ownership and
+   accountability that AI tools cannot bear. Some AI coding tools
+   default to injecting `Co-Authored-By` — override or remove it.
+
+### Trailer Format
+
+```
+Signed-off-by: Full Name <email@example.com>
+Assisted-by: Claude Sonnet 4.6 (via Claude Code)
+```
+
+- Blank line before trailers
+- No blank lines between trailers
+- No trailing blank lines
+
+## User Confirmation
+
+**CRITICAL RULE**: Always display the full commit message and wait for
+explicit user approval before executing `git commit`.
+
+## Commit Execution
+
+Use heredoc format for multi-line messages:
+
+```bash
+git commit -m "$(cat <<'EOF'
+<type>(<scope>): <description>
+
+<body>
+
+Signed-off-by: Name <email>
+Assisted-by: Model (via Tool)
+EOF
+)"
+```
+
+**Never use**: `--no-verify`, `--no-gpg-sign`, or `--amend`
+(unless the user explicitly requests it).
+
+## Examples
+
+### Feature with component scope
+
+```
+feat(config): add enforcedConfigLevel validation
+
+Validate that enforcedConfigLevel is one of the three allowed values
+(global, namespace, resource) during ConfigMap admission. Previously
+invalid values were silently accepted.
+
+Signed-off-by: Jane Developer <jane@example.com>
+Assisted-by: Claude Sonnet 4.6 (via Claude Code)
+```
+
+### Bug fix closing an issue
+
+```
+fix(controller): prevent duplicate TTL annotations on PipelineRuns
+
+The reconciler was setting TTL annotations on every reconcile loop
+even when the annotation already existed with the correct value.
+This caused unnecessary API writes and noisy audit logs.
+
+Fixes #42
+
+Signed-off-by: John Developer <john@example.com>
+Assisted-by: Claude Sonnet 4.6 (via Claude Code)
+```
+
+### Documentation update
+
+```
+docs(tutorials): add resource-group selector examples
+
+Signed-off-by: Jane Developer <jane@example.com>
+```
+
+### Breaking change
+
+```
+feat(config)!: rename historyLimit to retentionLimit
+
+BREAKING CHANGE: The ConfigMap field `historyLimit` is now
+`retentionLimit`. Update your tekton-pruner-default-spec ConfigMap
+before upgrading.
+
+Signed-off-by: John Developer <john@example.com>
+Assisted-by: Claude Sonnet 4.6 (via Claude Code)
+```
+
+## Auto-Detection Summary
+
+When generating commit messages:
+
+1. Run `git status` (without `-uall` flag)
+2. Run `git diff --cached` for staged changes
+3. Identify primary component from staged file paths
+4. If scope unclear, ask user
+5. If user mentions a GitHub issue, add `Fixes #NNN` to body
+6. Analyze staged files to determine commit type
+7. Generate scope and description
+8. Detect author info from env vars or git config
+9. Ensure subject line is ≤50 characters (max 72)
+10. Wrap body text at 72 characters per line
+11. Add required trailers (`Signed-off-by` and `Assisted-by`)
+12. **Display message and ask for user confirmation**
+13. Only commit after receiving confirmation
+
+## Additional Resources
+
+- **`references/commit-types.md`** — complete type reference with examples
+- [Tekton community conventions](https://github.com/tektoncd/community/blob/main/standards.md#commit-messages)