fix(context-sync): short-circuit when root AGENT.md is unreachable

In CI's clean checkout the tree-walk for ~/dev/.context/AGENT.md
finds nothing, leaving ROOT_CONTEXT empty. The script previously
proceeded to regenerate AGENTS.md, .cursorrules,
.aider.conventions.md, and .context/system-prompt.txt as
project-only — but the committed versions are root+project, so
the drift gate added in cc401d9 fails CI on every push.

When no root context is reachable, only regenerate CLAUDE.md
(which is project-only by design — Claude Code walks up the tree
itself to find the root). The root-bearing adapters are left
untouched, eliminating the false-positive drift.

Local runs (with root context reachable) are unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/context-sync.sh

@@ -39,7 +39,17 @@ fi
 if [ -n "$ROOT_CONTEXT" ] && [ -f "$ROOT_CONTEXT" ]; then
   echo "  Root context: $ROOT_CONTEXT"
 else
-  echo "  No root AGENT.md found (project context only)"
+  # No reachable root AGENT.md — common in CI's clean checkout. The root+project
+  # adapters (AGENTS.md, .cursorrules, .aider.conventions.md, system-prompt.txt)
+  # require the root context to regenerate correctly, so we skip them entirely
+  # and only regenerate CLAUDE.md (which is project-only and inherits root via
+  # tree walk in Claude Code itself).
+  echo "  No root AGENT.md found — regenerating CLAUDE.md only"
+  echo "Syncing project context from $PROJECT_FILE..."
+  cat "$PROJECT_FILE" > CLAUDE.md
+  echo "  → CLAUDE.md (project-only)"
+  echo "Done."
+  exit 0
 fi
 
 # Emit root context + separator