fix: auto-trigger polish release notes on release publish (Fission-AI#519)

* perf: add path filtering to Nix validation CI job

Skip Nix flake validation when no Nix-related files change. This speeds
up CI for PRs that only touch source code, docs, or tests.

Files that trigger Nix validation:
- flake.nix, flake.lock
- package.json, pnpm-lock.yaml
- scripts/update-flake.sh
- .github/workflows/ci.yml

Uses dorny/paths-filter@v3 for change detection. Required-checks jobs
updated to handle skipped status correctly.

* fix: auto-trigger polish release notes on release publish

The workflow was only set up for manual dispatch, requiring someone to
remember to run it after each release. This change adds an automatic
trigger on `release: [published]` events while keeping the manual
trigger as a fallback.

The Claude Code Action supports any GitHub event when using the `prompt`
parameter for custom automations.

Author: TabishB

.github/workflows/polish-release-notes.yml

@@ -1,15 +1,24 @@
 name: Polish Release Notes
 
-# Manual trigger after a release is published
-# The Claude Code action doesn't support 'release' event triggers directly
+# Automatically polish release notes when a release is published.
+# Also supports manual trigger as a fallback.
+#
+# Note: The Claude Code Action works with any GitHub event when using the
+# `prompt` parameter for custom automations. If release triggers stop working,
+# check https://github.com/anthropics/claude-code-action for updates.
 on:
+  release:
+    types: [published]
   workflow_dispatch:
     inputs:
       tag_name:
         description: 'Release tag to polish (e.g., v0.18.0)'
         required: true
         type: string
 
+env:
+  TAG_NAME: ${{ github.event.release.tag_name || inputs.tag_name }}
+
 permissions:
   contents: write
 
@@ -27,8 +36,8 @@ jobs:
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          gh release view "${{ inputs.tag_name }}" --json body -q '.body' > current-notes.md
-          echo "Fetched release notes for ${{ inputs.tag_name }}"
+          gh release view "${{ env.TAG_NAME }}" --json body -q '.body' > current-notes.md
+          echo "Fetched release notes for ${{ env.TAG_NAME }}"
 
       - name: Transform release notes with Claude
         uses: anthropics/claude-code-action@v1
@@ -38,7 +47,7 @@ jobs:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           claude_args: "--allowedTools Write,Read"
           prompt: |
-            Transform the changelog in `current-notes.md` into release notes for OpenSpec ${{ inputs.tag_name }}.
+            Transform the changelog in `current-notes.md` into release notes for OpenSpec ${{ env.TAG_NAME }}.
 
             ## Voice
 
@@ -55,7 +64,7 @@ jobs:
 
             A short title in this format:
             ```
-            ${{ inputs.tag_name }} - [1-4 words describing the release]
+            ${{ env.TAG_NAME }} - [1-4 words describing the release]
             ```
 
             Examples:
@@ -72,7 +81,7 @@ jobs:
             ### 2. `polished-notes.md`
 
             ```markdown
-            ## What's New in ${{ inputs.tag_name }}
+            ## What's New in ${{ env.TAG_NAME }}
 
             [One sentence: what's the theme of this release?]
 
@@ -129,7 +138,7 @@ jobs:
         env:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          TAG="${{ inputs.tag_name }}"
+          TAG="${{ env.TAG_NAME }}"
 
           if [ -f "polished-notes.md" ] && [ -f "release-title.txt" ]; then
             TITLE=$(cat release-title.txt)