docs: RFC 0051 portable hook binary resolution

Problem: Claude Code hooks run in minimal environment without PATH.
Commands by name hang; only full paths work.

Solution: Use $CLAUDE_PROJECT_DIR for portable binary resolution:
  "$CLAUDE_PROJECT_DIR/target/release/blue" guard --path="$FILE_PATH"

This is documented Claude Code behavior - hooks don't inherit shell
initialization for security reasons.

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

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

@@ -0,0 +1,165 @@
+# RFC 0051: Portable Hook Binary Resolution
+
+**Status**: Draft
+**Created**: 2026-02-01
+**Author**: Claude Opus 4.5
+**Related**: RFC 0038, RFC 0049
+
+## Problem Statement
+
+Claude Code PreToolUse hooks run in a minimal environment without full PATH initialization. When hooks invoke commands by name (e.g., `blue guard`), the shell cannot resolve the binary and hangs indefinitely.
+
+### Current Workaround
+
+The guard hook uses a hardcoded absolute path:
+```bash
+/Users/ericg/letemcook/blue/target/release/blue guard --path="$FILE_PATH"
+```
+
+This works but is:
+- **Not portable**: Different paths on different machines
+- **Fragile**: Breaks if binary moves
+- **Not team-friendly**: Each developer needs different paths
+
+### Root Cause
+
+Hook processes don't inherit the user's shell initialization (`.bashrc`, `.zshrc`). This means:
+- Custom PATH entries (like `~/.cargo/bin`) are not available
+- Homebrew paths may be missing
+- Language version managers (nvm, rbenv) don't work
+
+This is likely intentional for security (preventing secrets/aliases in hooks).
+
+## Proposed Solution
+
+Use `$CLAUDE_PROJECT_DIR` environment variable for portable binary resolution.
+
+### Option A: Project-Relative Binary (Recommended)
+
+Update hook to use `$CLAUDE_PROJECT_DIR`:
+
+```bash
+#!/bin/bash
+# .claude/hooks/guard-write.sh
+
+FILE_PATH=$(jq -r '.tool_input.file_path // empty')
+
+if [ -z "$FILE_PATH" ]; then
+    exit 0
+fi
+
+# Use CLAUDE_PROJECT_DIR for portable path resolution
+"$CLAUDE_PROJECT_DIR/target/release/blue" guard --path="$FILE_PATH"
+```
+
+**Pros:**
+- Portable across team members
+- Works with any checkout location
+- Documented Claude Code pattern
+
+**Cons:**
+- Requires binary in project directory
+- Must rebuild after checkout
+
+### Option B: SessionStart PATH Injection
+
+Add a SessionStart hook that adds blue to PATH:
+
+```json
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "hooks": [{
+          "type": "command",
+          "command": ".claude/hooks/setup-path.sh"
+        }]
+      }
+    ]
+  }
+}
+```
+
+```bash
+#!/bin/bash
+# .claude/hooks/setup-path.sh
+if [ -n "$CLAUDE_ENV_FILE" ]; then
+  echo "export PATH=\"$CLAUDE_PROJECT_DIR/target/release:\$PATH\"" >> "$CLAUDE_ENV_FILE"
+fi
+exit 0
+```
+
+**Pros:**
+- `blue` works by name in all subsequent hooks
+- Cleaner hook scripts
+
+**Cons:**
+- Requires SessionStart hook
+- More complex setup
+- Session-specific (resets on restart)
+
+### Option C: Installed Binary with Explicit PATH
+
+For teams that install blue globally:
+
+```bash
+#!/bin/bash
+# Explicitly set PATH to include common install locations
+export PATH="$HOME/.cargo/bin:/usr/local/bin:$PATH"
+
+FILE_PATH=$(jq -r '.tool_input.file_path // empty')
+if [ -z "$FILE_PATH" ]; then
+    exit 0
+fi
+
+blue guard --path="$FILE_PATH"
+```
+
+**Pros:**
+- Works with installed binaries
+- Standard Unix pattern
+
+**Cons:**
+- Must enumerate all possible install locations
+- Still not fully portable
+
+## Recommendation
+
+**Option A** (project-relative binary) is recommended because:
+1. It's documented by Claude Code
+2. It's portable across machines
+3. It doesn't require additional hooks
+4. It works with the existing build workflow
+
+## Implementation Plan
+
+- [ ] Update `.claude/hooks/guard-write.sh` to use `$CLAUDE_PROJECT_DIR`
+- [ ] Update `.claude/settings.json` to use quoted project dir path
+- [ ] Test on fresh checkout
+- [ ] Document in README or CONTRIBUTING.md
+
+## Migration
+
+Before:
+```bash
+/Users/ericg/letemcook/blue/target/release/blue guard --path="$FILE_PATH"
+```
+
+After:
+```bash
+"$CLAUDE_PROJECT_DIR/target/release/blue" guard --path="$FILE_PATH"
+```
+
+## Testing
+
+1. Clone repo to new location
+2. Build: `cargo build --release -p blue`
+3. Run Claude Code
+4. Attempt a write operation
+5. Verify guard runs without hanging
+
+## References
+
+- Claude Code Hooks Documentation: https://code.claude.com/docs/en/hooks.md
+- RFC 0038: SDLC Workflow Discipline
+- RFC 0049: Synchronous Guard Command