feat: P2P sharing layer (share, receive, relay)

plugins/alive/hooks/hooks.json

@@ -1,5 +1,5 @@
 {
-  "description": "ALIVE Context System v2 — 14 hooks. Session hooks read/write .alive/_squirrels/. All read stdin JSON for session_id.",
+  "description": "ALIVE Context System v2 — 15 hooks. Session hooks read/write .alive/_squirrels/. All read stdin JSON for session_id.",
   "hooks": {
     "SessionStart": [
       {
@@ -14,6 +14,11 @@
             "type": "command",
             "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/scripts/alive-repo-detect.sh",
             "timeout": 10
+          },
+          {
+            "type": "command",
+            "command": "bash ${CLAUDE_PLUGIN_ROOT}/hooks/scripts/alive-relay-check.sh",
+            "timeout": 10
           }
         ]
       },

plugins/alive/hooks/scripts/alive-log-guardian.sh

@@ -22,10 +22,13 @@ if [ -n "${WORLD_ROOT:-}" ] && ! echo "$FILE_PATH" | grep -q "^$WORLD_ROOT"; the
   exit 0
 fi
 
-# Block ALL Write operations to log.md (must use Edit to prepend)
+# Block Write operations to existing log.md (must use Edit to prepend)
+# Allow Write to non-existent log.md (new walnut creation)
 if [ "$TOOL_NAME" = "Write" ]; then
-  echo '{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"deny","permissionDecisionReason":"log.md cannot be overwritten. Use Edit to prepend new entries after the YAML frontmatter."}}'
-  exit 0
+  if [ -f "$FILE_PATH" ]; then
+    echo '{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"deny","permissionDecisionReason":"log.md cannot be overwritten. Use Edit to prepend new entries after the YAML frontmatter."}}'
+    exit 0
+  fi
 fi
 
 # For Edit: check if the old_string contains a signed entry

plugins/alive/hooks/scripts/alive-relay-check.sh

@@ -0,0 +1,62 @@
+#!/bin/bash
+# Hook: Relay Check -- SessionStart (startup)
+# Probes the GitHub relay for pending .walnut packages and injects a
+# notification into the session. Silent when no relay configured or no
+# pending packages. Exits 0 on ANY error.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+source "$SCRIPT_DIR/alive-common.sh"
+
+# Read stdin JSON -- extracts session_id, cwd, event name
+read_hook_input
+
+# Find world root (needed for alive-common.sh contract, though relay
+# config lives at $HOME/.alive/relay/ not under the world)
+find_world || exit 0
+
+# Fast path: no relay configured -- exit immediately
+RELAY_DIR="$HOME/.alive/relay"
+RELAY_CONFIG="$RELAY_DIR/relay.json"
+[ -f "$RELAY_CONFIG" ] || exit 0
+
+# Resolve relay-probe.py location
+PLUGIN_ROOT="${CLAUDE_PLUGIN_ROOT:-$(cd "$SCRIPT_DIR/../.." && pwd)}"
+PROBE_SCRIPT="$PLUGIN_ROOT/scripts/relay-probe.py"
+[ -f "$PROBE_SCRIPT" ] || exit 0
+
+# Run probe -- writes state.json atomically. Errors are swallowed by
+# relay-probe.py internally (it always exits 0).
+STATE_JSON="$RELAY_DIR/state.json"
+python3 "$PROBE_SCRIPT" --config "$RELAY_CONFIG" --state "$STATE_JSON" 2>/dev/null || exit 0
+
+# Read pending_packages from state.json via inline python3
+# (json_field reads HOOK_INPUT, not arbitrary files)
+PENDING=$(python3 -c "
+import json, sys
+try:
+    with open('$STATE_JSON') as f:
+        print(json.load(f).get('pending_packages', 0))
+except Exception:
+    print(0)
+" 2>/dev/null || echo 0)
+
+# Silent exit if nothing pending
+[ "$PENDING" -gt 0 ] 2>/dev/null || exit 0
+
+# Build notification
+MSG="You have ${PENDING} walnut package(s) waiting. Run /alive:receive to import."
+ESCAPED=$(escape_for_json "$MSG")
+
+cat <<HOOKEOF
+{
+  "additional_context": "${ESCAPED}",
+  "hookSpecificOutput": {
+    "hookEventName": "SessionStart",
+    "additionalContext": "${ESCAPED}"
+  }
+}
+HOOKEOF
+
+exit 0