feat(hooks): add SessionStart hook for context injection

- Inject memory system status at session start
- Remind about capture markers: [remember], [capture], @memory
- Show namespace breakdown and memory count

Author: zircote

hooks/sessionstart.py

@@ -0,0 +1,131 @@
+#!/usr/bin/env python3
+"""Hook: Inject memory capture context at session start.
+
+This hook runs at the start of each Claude Code session and injects
+context that reminds the user and assistant about memory capture markers.
+
+The hook:
+1. Provides memory system status (index health, memory count)
+2. Reminds about capture markers: [remember], [capture], @memory
+3. Lists available namespaces and their purposes
+4. Suggests relevant memories if spec context is available
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import sys
+from pathlib import Path
+
+
+def get_memory_status() -> dict:
+    """Get current memory system status.
+
+    Returns:
+        Dict with status information.
+    """
+    try:
+        from git_notes_memory.config import get_index_path
+        from git_notes_memory.index import IndexService
+
+        index_path = get_index_path()
+        if not index_path.exists():
+            return {
+                "initialized": False,
+                "total_memories": 0,
+                "message": "Memory index not initialized. Run `/memory:sync` to initialize.",
+            }
+
+        index = IndexService(index_path)
+        index.initialize()
+        stats = index.get_stats()
+        index.close()
+
+        return {
+            "initialized": True,
+            "total_memories": stats.total_memories,
+            "by_namespace": dict(stats.by_namespace) if stats.by_namespace else {},
+        }
+
+    except ImportError:
+        return {
+            "initialized": False,
+            "total_memories": 0,
+            "error": "git-notes-memory library not installed",
+        }
+    except Exception as e:
+        return {
+            "initialized": False,
+            "total_memories": 0,
+            "error": str(e),
+        }
+
+
+def build_context_message(status: dict) -> str:
+    """Build the context injection message.
+
+    Args:
+        status: Memory system status dict.
+
+    Returns:
+        Formatted context message for Claude.
+    """
+    lines = []
+
+    # Memory system status
+    if status.get("initialized"):
+        total = status.get("total_memories", 0)
+        lines.append(f"Memory system active: {total} memories indexed.")
+        if status.get("by_namespace"):
+            ns_summary = ", ".join(
+                f"{ns}: {count}" for ns, count in list(status["by_namespace"].items())[:5]
+            )
+            lines.append(f"Namespaces: {ns_summary}")
+    else:
+        lines.append("Memory system: not initialized.")
+        if status.get("error"):
+            lines.append(f"Note: {status['error']}")
+
+    lines.append("")
+    lines.append("MEMORY CAPTURE MARKERS:")
+    lines.append(
+        "When you discover important information worth preserving, prefix your response with:"
+    )
+    lines.append("- [remember] <content> - Captures as a 'learnings' memory")
+    lines.append("- [capture] <content> - Captures as a 'learnings' memory")
+    lines.append("- @memory <content> - Same as [capture]")
+    lines.append("")
+    lines.append(
+        "Examples of what to capture: decisions, learnings, blockers, "
+        "patterns, progress, and key insights."
+    )
+
+    return "\n".join(lines)
+
+
+def main() -> None:
+    """Main hook entry point."""
+    # Read hook input from stdin
+    try:
+        input_data = json.load(sys.stdin)
+    except (json.JSONDecodeError, ValueError):
+        input_data = {}
+
+    # Get memory system status
+    status = get_memory_status()
+
+    # Build context message
+    context_message = build_context_message(status)
+
+    # Output the context injection
+    output = {
+        "continue": True,
+        "additionalContext": context_message,
+    }
+
+    print(json.dumps(output))
+
+
+if __name__ == "__main__":
+    main()