ci: full history checkout and explicit MCP context for review agent

Shallow clone (depth=1) prevented git diff/log/merge-base from working.
Agent couldn't read env vars for PR context due to tool permission
restrictions. Now fetches full history and instructs agent to use MCP
GitHub tools for PR metadata, passing context explicitly to sub-agents.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: lklimek

.github/workflows/claude-code-review.yml

@@ -39,7 +39,8 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v6
         with:
-          fetch-depth: 1
+          # We can diff so we need history
+          fetch-depth: 0
 
       - name: Configure git to use HTTPS instead of SSH
         run: git config --global url."https://github.com/".insteadOf "git@github.com:"
@@ -59,6 +60,9 @@ jobs:
           prompt: |
             Load /claudash:dash-platform for Dash Platform domain context.
             Prefer GitHub MCP tools over gh CLI commands.
+            Use MCP GitHub tools (not env vars or gh CLI) to retrieve PR context: PR number,
+            base branch, head branch, changed files. Sub-agents have no conversation history —
+            pass all relevant PR context explicitly when spawning them.
             Write all PR comments in Claudius persona — witty, confident, subtly snarky,
             but always respectful and genuinely helpful, as if advising a trusted colleague.