feat: RFC 0051 SessionStart hook for PATH injection

Added SessionStart hook that adds $CLAUDE_PROJECT_DIR/target/release
to PATH via CLAUDE_ENV_FILE. This makes `blue` available by name in
all subsequent hooks.

- .claude/hooks/session-start.sh: Sets PATH on session start
- .claude/hooks/guard-write.sh: Now uses `blue` instead of full path
- .claude/settings.json: Added SessionStart hook

Requires Claude Code restart to take effect.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.blue/docs/rfcs/0051-portable-hook-binary-resolution.draft.md

@@ -125,11 +125,11 @@ blue guard --path="$FILE_PATH"
 
 ## Recommendation
 
-**Option A** (project-relative binary) is recommended because:
-1. It's documented by Claude Code
-2. It's portable across machines
-3. It doesn't require additional hooks
-4. It works with the existing build workflow
+**Option B** (SessionStart PATH injection) is recommended because:
+1. Cleaner hook scripts - just use `blue` by name
+2. Works for any hook that needs blue
+3. Consistent with existing SessionStart hooks pattern
+4. PATH set once, used everywhere
 
 ## Implementation Plan
 

.claude/hooks/guard-write.sh

@@ -10,5 +10,5 @@ if [ -z "$FILE_PATH" ]; then
 fi
 
 # Call blue guard with the extracted path
-# Note: Full path required - PATH lookup hangs in Claude Code hook environment
-/Users/ericg/letemcook/blue/target/release/blue guard --path="$FILE_PATH"
+# RFC 0051: PATH is set by SessionStart hook
+blue guard --path="$FILE_PATH"

.claude/hooks/session-start.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+# SessionStart hook - sets up PATH for blue CLI
+# RFC 0051: Portable hook binary resolution
+
+if [ -n "$CLAUDE_ENV_FILE" ] && [ -n "$CLAUDE_PROJECT_DIR" ]; then
+  echo "export PATH=\"\$CLAUDE_PROJECT_DIR/target/release:\$PATH\"" >> "$CLAUDE_ENV_FILE"
+fi
+
+exit 0

.claude/settings.json

@@ -1,5 +1,15 @@
 {
   "hooks": {
+    "SessionStart": [
+      {
+        "hooks": [
+          {
+            "type": "command",
+            "command": ".claude/hooks/session-start.sh"
+          }
+        ]
+      }
+    ],
     "PreToolUse": [
       {
         "matcher": "Write|Edit|MultiEdit",