Add standalone code-review skill with maintainer-sourced review rules

.github/copilot-instructions.md

@@ -90,6 +90,18 @@ Major test projects:
 
 Find all tests: `find . -name "*.UnitTests.csproj"`
 
+### CI Pipelines (Azure DevOps)
+
+When referencing or triggering CI pipelines, use these current pipeline names:
+
+| Pipeline | Name | Purpose |
+|----------|------|---------|
+| Overall CI | `maui-pr` | Full PR validation build |
+| Device Tests | `maui-pr-devicetests` | Helix-based device tests |
+| UI Tests | `maui-pr-uitests` | Appium-based UI tests |
+
+**⚠️ Old pipeline names** (e.g., `MAUI-UITests-public`, `MAUI-public`) are **outdated** and should NOT be used. Always use the names above.
+
 ### Code Formatting
 
 Always format code before committing:
@@ -126,26 +138,6 @@ When working with public API changes:
 - **Use `dotnet format analyzers`** if having trouble
 - **If files are incorrect**: Revert all changes, then add only the necessary new API entries
 
-**🚨 CRITICAL: `#nullable enable` must be line 1**
-
-Every `PublicAPI.Unshipped.txt` file starts with `#nullable enable` (often BOM-prefixed: `#nullable enable`) on the **first line**. If this line is moved or removed, the analyzer treats it as a declared API symbol and emits **RS0017** errors.
-
-**Never sort these files with plain `sort`** — the BOM bytes (`0xEF 0xBB 0xBF`) sort after ASCII characters under `LC_ALL=C`, pushing `#nullable enable` to the bottom of the file.
-
-When resolving merge conflicts or adding entries, use this safe pattern that preserves line 1:
-```bash
-for f in $(git diff --name-only --diff-filter=U | grep "PublicAPI.Unshipped.txt"); do
-  # Extract and preserve the #nullable enable line (with or without BOM)
-  HEADER=$(head -1 "$f" | grep -o '.*#nullable enable' || echo '#nullable enable')
-  # Strip conflict markers, remove all #nullable lines, sort+dedup the API entries
-  grep -v '^<<<<<<\|^======\|^>>>>>>\|#nullable enable' "$f" | LC_ALL=C sort -u | sed '/^$/d' > /tmp/api_fix.txt
-  # Reassemble: header first, then sorted entries
-  printf '%s\n' "$HEADER" > "$f"
-  cat /tmp/api_fix.txt >> "$f"
-  git add "$f"
-done
-```
-
 ### Branching
 - `main` - For bug fixes without API changes
 - `net10.0` - For new features and API changes
@@ -189,16 +181,23 @@ git commit -m "Fix: Description of the change"
 2. Exception: If the user's instructions explicitly include pushing, proceed without asking.
 
 ### Documentation
-
 - Update XML documentation for public APIs
 - Follow existing code documentation patterns
 - Update relevant docs in `docs/` folder when needed
 
-**Platform-Specific Documentation:**
-- `.github/instructions/safe-area-ios.instructions.md` - Safe area investigation (iOS/macCatalyst)
-- `.github/instructions/uitests.instructions.md` - UI test guidelines (includes safe area testing section)
-- `.github/instructions/android.instructions.md` - Android handler implementation
-- `.github/instructions/xaml-unittests.instructions.md` - XAML unit test guidelines
+### Opening PRs
+
+All PRs are required to have this at the top of the description:
+
+```
+<!-- Please let the below note in for people that find this PR -->
+> [!NOTE]
+> Are you waiting for the changes in this PR to be merged?
+> It would be very helpful if you could [test the resulting artifacts](https://github.com/dotnet/maui/wiki/Testing-PR-Builds) from this PR and let us know in a comment if this change resolves your issue. Thank you!
+```
+
+Always put that at the top, without the block quotes. Without it, users will NOT be able to try the PR and your work will have been in vain!
+
 
 
 ## Custom Agents and Skills
@@ -216,18 +215,24 @@ The repository includes specialized custom agents and reusable skills for specif
 
 ### Available Custom Agents
 
-1. **write-tests-agent** - Agent for writing tests. Determines test type (UI vs XAML) and invokes the appropriate skill (`write-ui-tests`, `write-xaml-tests`)
+1. **pr** - Sequential 4-phase workflow for reviewing and working on PRs
+   - **Use when**: A PR already exists and needs review or work, OR an issue needs a fix
+   - **Capabilities**: PR review, test verification, fix exploration, alternative comparison
+   - **Trigger phrases**: "review PR #XXXXX", "work on PR #XXXXX", "fix issue #XXXXX", "continue PR #XXXXX"
+   - **Do NOT use for**: Just running tests manually → Use `sandbox-agent`
+
+2. **write-tests-agent** - Agent for writing tests. Determines test type (UI vs XAML) and invokes the appropriate skill (`write-ui-tests`, `write-xaml-tests`)
    - **Use when**: Creating new tests for issues or PRs
    - **Capabilities**: Test type determination (UI and XAML), skill invocation, test verification
    - **Trigger phrases**: "write tests for #XXXXX", "create tests", "add test coverage"
 
-2. **sandbox-agent** - Specialized agent for working with the Sandbox app for testing, validation, and experimentation
+3. **sandbox-agent** - Specialized agent for working with the Sandbox app for testing, validation, and experimentation
    - **Use when**: User wants to manually test PR functionality or reproduce issues
    - **Capabilities**: Sandbox app setup, Appium-based manual testing, PR functional validation
    - **Trigger phrases**: "test this PR", "validate PR #XXXXX in Sandbox", "reproduce issue #XXXXX", "try out in Sandbox"
-   - **Do NOT use for**: Code review (use `pr-review` skill), writing automated tests (use write-tests-agent)
+   - **Do NOT use for**: Code review (use pr agent), writing automated tests (use write-tests-agent)
 
-3. **learn-from-pr** - Extracts lessons from PRs and applies improvements to the repository
+4. **learn-from-pr** - Extracts lessons from PRs and applies improvements to the repository
    - **Use when**: After complex PR, want to improve instruction files/skills based on lessons learned
    - **Capabilities**: Analyzes PR, identifies failure modes, applies improvements to instruction files, skills, code comments
    - **Trigger phrases**: "learn from PR #XXXXX and apply improvements", "improve repo based on what we learned", "update skills based on PR"
@@ -240,90 +245,79 @@ Skills are modular capabilities that can be invoked directly or used by agents.
 
 #### User-Facing Skills
 
-1. **pr-review** (`.github/skills/pr-review/SKILL.md`)
-   - **Purpose**: End-to-end PR review orchestrator — follows phase instructions: pr-preflight, pr-gate, try-fix, pr-report
-   - **Trigger phrases**: "review PR #XXXXX", "work on PR #XXXXX", "fix issue #XXXXX", "continue PR #XXXXX"
-   - **Capabilities**: Multi-model fix exploration, test verification, alternative comparison, PR review recommendation
-   - **Do NOT use for**: Just running tests manually → Use `sandbox-agent`
-   - **Phase instructions** (in `.github/pr-review/`):
-     - `pr-preflight.md` — Context gathering from issue/PR
-     - `pr-gate.md` — Verify tests FAIL without fix, PASS with fix
-     - `pr-report.md` — Final recommendation
-   - **Phase skill**: `try-fix` — Multi-model fix exploration
-
-3. **issue-triage** (`.github/skills/issue-triage/SKILL.md`)
+1. **issue-triage** (`.github/skills/issue-triage/SKILL.md`)
    - **Purpose**: Query and triage open issues that need milestones, labels, or investigation
    - **Trigger phrases**: "find issues to triage", "show me old Android issues", "what issues need attention"
    - **Scripts**: `init-triage-session.ps1`, `query-issues.ps1`, `record-triage.ps1`
 
-4. **find-reviewable-pr** (`.github/skills/find-reviewable-pr/SKILL.md`)
+2. **find-reviewable-pr** (`.github/skills/find-reviewable-pr/SKILL.md`)
    - **Purpose**: Finds open PRs in dotnet/maui and dotnet/docs-maui that need review
    - **Trigger phrases**: "find PRs to review", "show milestoned PRs", "find partner PRs"
    - **Scripts**: `query-reviewable-prs.ps1`
    - **Categories**: P/0, milestoned, partner, community, recent, docs-maui
 
-5. **pr-finalize** (`.github/skills/pr-finalize/SKILL.md`)
+3. **pr-finalize** (`.github/skills/pr-finalize/SKILL.md`)
    - **Purpose**: Verifies PR title and description match actual implementation, AND performs code review for best practices before merge.
    - **Trigger phrases**: "finalize PR #XXXXX", "check PR description for #XXXXX", "review commit message"
    - **Used by**: Before merging any PR, when description may be stale
    - **Note**: Does NOT require agent involvement or session markdown - works on any PR
    - **🚨 CRITICAL**: NEVER use `--approve` or `--request-changes` - only post comments. Approval is a human decision.
 
-6. **learn-from-pr** (`.github/skills/learn-from-pr/SKILL.md`)
+4. **code-review** (`.github/skills/code-review/SKILL.md`)
+   - **Purpose**: Reviews PR code changes for correctness, safety, and consistency with MAUI conventions. Walks through a MAUI-specific checklist covering handler lifecycle, platform code, safe area, threading, public API, and test patterns.
+   - **Trigger phrases**: "review code for PR #XXXXX", "code review PR #XXXXX", "review this PR's code"
+   - **Note**: Standalone skill — uses independence-first assessment (reads code before PR description to avoid anchoring bias). Can be used by any agent or invoked directly.
+   - **🚨 CRITICAL**: NEVER use `--approve` or `--request-changes` — only post comments. Approval is a human decision.
+
+5. **learn-from-pr** (`.github/skills/learn-from-pr/SKILL.md`)
    - **Purpose**: Analyzes completed PR to identify repository improvements (analysis only, no changes applied)
    - **Trigger phrases**: "what can we learn from PR #XXXXX?", "how can we improve agents based on PR #XXXXX?"
    - **Used by**: After complex PRs, when agent struggled to find solution
    - **Output**: Prioritized recommendations for instruction files, skills, code comments
    - **Note**: For applying changes automatically, use the learn-from-pr agent instead
 
-7. **write-ui-tests** (`.github/skills/write-ui-tests/SKILL.md`)
+6. **write-ui-tests** (`.github/skills/write-ui-tests/SKILL.md`)
    - **Purpose**: Creates UI tests for GitHub issues and verifies they reproduce the bug
    - **Trigger phrases**: "write UI tests for #XXXXX", "create UI test for issue", "add UI test coverage"
    - **Output**: Test files that fail without fix, pass with fix
 
-8. **write-xaml-tests** (`.github/skills/write-xaml-tests/SKILL.md`)
+7. **write-xaml-tests** (`.github/skills/write-xaml-tests/SKILL.md`)
    - **Purpose**: Creates XAML unit tests for XAML parsing, compilation, and source generation
    - **Trigger phrases**: "write XAML tests for #XXXXX", "test XamlC behavior", "reproduce XAML parsing bug"
    - **Output**: Test files for Controls.Xaml.UnitTests
 
-9. **verify-tests-fail-without-fix** (`.github/skills/verify-tests-fail-without-fix/SKILL.md`)
+8. **verify-tests-fail-without-fix** (`.github/skills/verify-tests-fail-without-fix/SKILL.md`)
    - **Purpose**: Verifies UI tests catch the bug before fix and pass with fix
    - **Two modes**: Verify failure only (test creation) or full verification (test + fix)
    - **Used by**: After creating tests, before considering PR complete
 
-10. **azdo-build-investigator** (`.github/skills/azdo-build-investigator/SKILL.md`)
-   - **Purpose**: Investigates CI failures for PRs — build errors, Helix test logs, and binlog analysis. Delegates to the `ci-analysis` skill from the dotnet/arcade-skills plugin.
-   - **Trigger phrases**: "check build for PR #XXXXX", "why did PR build fail", "get build status", "what's failing on PR", "Helix failures"
+9. **pr-build-status** (`.github/skills/pr-build-status/SKILL.md`)
+   - **Purpose**: Retrieves Azure DevOps build information for PRs (build IDs, stage status, failed jobs)
+   - **Trigger phrases**: "check build for PR #XXXXX", "why did PR build fail", "get build status"
    - **Used by**: When investigating CI failures
 
-11. **run-integration-tests** (`.github/skills/run-integration-tests/SKILL.md`)
+10. **run-integration-tests** (`.github/skills/run-integration-tests/SKILL.md`)
    - **Purpose**: Build, pack, and run .NET MAUI integration tests locally
    - **Trigger phrases**: "run integration tests", "test templates locally", "run macOSTemplates tests", "run RunOniOS tests"
    - **Categories**: Build, WindowsTemplates, macOSTemplates, Blazor, MultiProject, Samples, AOT, RunOnAndroid, RunOniOS
    - **Note**: **ALWAYS use this skill** instead of manual `dotnet test` commands for integration tests
 
-12. **evaluate-pr-tests** (`.github/skills/evaluate-pr-tests/SKILL.md`)
-   - **Purpose**: Evaluates tests added in a PR for coverage, quality, edge cases, and test type appropriateness
-   - **Trigger phrases**: "evaluate tests in PR #XXXXX", "review test quality", "are these tests good enough", "check test coverage"
-   - **Scripts**: `Gather-TestContext.ps1`
-   - **Checks**: Fix coverage, edge case gaps, test type preference (unit > device > UI), conventions, flakiness risk, duplicate coverage, platform scope, assertion quality
-
-#### Internal Skills (Used by Skills/Agents)
+#### Internal Skills (Used by Agents)
 
-12. **try-fix** (`.github/skills/try-fix/SKILL.md`)
+11. **try-fix** (`.github/skills/try-fix/SKILL.md`)
    - **Purpose**: Proposes ONE independent fix approach, applies it, tests, records result with failure analysis, then reverts
-   - **Used by**: `pr-review` skill Phase 3 (Try-Fix phase) - rarely invoked directly by users
+   - **Used by**: pr agent Phase 3 (Fix phase) - rarely invoked directly by users
    - **Behavior**: Reads prior attempts to learn from failures. Max 5 attempts per session.
    - **Output**: Updates session markdown with attempt results and failure analysis
 
-### Using Custom Agents and Skills
+### Using Custom Agents
 
-**Delegation Policy**: When user request matches skill/agent trigger phrases, **ALWAYS invoke the appropriate skill or delegate to the agent immediately**. Do not ask for permission or explain alternatives unless the request is ambiguous.
+**Delegation Policy**: When user request matches agent trigger phrases, **ALWAYS delegate to the appropriate agent immediately**. Do not ask for permission or explain alternatives unless the request is ambiguous.
 
 **Examples of correct delegation**:
-- User: "Review PR #12345" → Immediately invoke **pr-review** skill
+- User: "Review PR #12345" → Immediately invoke **pr** agent
 - User: "Test this PR" → Immediately invoke **sandbox-agent**
-- User: "Fix issue #67890" → Immediately invoke **pr-review** skill
+- User: "Fix issue #67890" (no PR exists) → Suggest using `/delegate` command
 - User: "Write tests for issue #12345" → Immediately invoke **write-tests-agent**
 
 **When NOT to delegate**: