feat(hooks): add gt block-pr-workflow command for PreToolUse hook

Implements infrastructure-level enforcement of the "no PRs" policy.
When a Claude Code agent tries to run `gh pr create`, `git checkout -b`,
or `git switch -c`, the PreToolUse hook calls this command which:

- Detects if we're in a Gas Town agent context (crew, polecat, etc.)
- If so, exits with code 2 to BLOCK the tool execution
- Outputs helpful guidance on what to do instead (push to main)

This makes the rule ironclad - agents can't create PRs even if they
try, because the hook intercepts and blocks before execution.

Hook configuration (add to .claude/settings.json):
  "PreToolUse": [{
    "matcher": "Bash(gh pr create*)",
    "hooks": [{"command": "gt block-pr-workflow --reason pr-create"}]
  }]

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

internal/cmd/block_pr_workflow.go

@@ -0,0 +1,106 @@
+package cmd
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+var blockPRWorkflowCmd = &cobra.Command{
+	Use:    "block-pr-workflow",
+	Hidden: true, // Internal command for Claude Code hooks
+	Short:  "Block PR workflow operations (hook helper)",
+	Long: `Block PR workflow operations in Gas Town.
+
+This command is called by Claude Code PreToolUse hooks to enforce the
+"no PRs" policy. Gas Town workers push directly to main - PRs add friction
+that breaks the autonomous execution model.
+
+Exit codes:
+  0 - Operation allowed (not in a restricted context)
+  2 - Operation BLOCKED (hook will prevent tool execution)
+
+The hook configuration in .claude/settings.json:
+  {
+    "PreToolUse": [{
+      "matcher": "Bash(gh pr create*)",
+      "hooks": [{"type": "command", "command": "gt block-pr-workflow --reason pr-create"}]
+    }]
+  }`,
+	RunE: runBlockPRWorkflow,
+}
+
+var blockPRReason string
+
+func init() {
+	blockPRWorkflowCmd.Flags().StringVar(&blockPRReason, "reason", "", "Reason for the block check (pr-create, feature-branch)")
+	rootCmd.AddCommand(blockPRWorkflowCmd)
+}
+
+func runBlockPRWorkflow(cmd *cobra.Command, args []string) error {
+	// Check if we're in a Gas Town agent context
+	// These env vars indicate we're running as a managed agent
+	isPolecat := os.Getenv("GT_POLECAT") != ""
+	isCrew := os.Getenv("GT_CREW") != ""
+	isWitness := os.Getenv("GT_WITNESS") != ""
+	isRefinery := os.Getenv("GT_REFINERY") != ""
+	isMayor := os.Getenv("GT_MAYOR") != ""
+	isDeacon := os.Getenv("GT_DEACON") != ""
+
+	// Also check if we're in a crew worktree by path
+	cwd, _ := os.Getwd()
+	inCrewWorktree := strings.Contains(cwd, "/crew/")
+	inPolecatWorktree := strings.Contains(cwd, "/polecats/")
+
+	isGasTownAgent := isPolecat || isCrew || isWitness || isRefinery || isMayor || isDeacon || inCrewWorktree || inPolecatWorktree
+
+	if !isGasTownAgent {
+		// Not in a Gas Town managed context - allow the operation
+		// This lets humans use PRs if they want
+		return nil
+	}
+
+	// We're in a Gas Town context - block PR operations
+	switch blockPRReason {
+	case "pr-create":
+		fmt.Fprintln(os.Stderr, "")
+		fmt.Fprintln(os.Stderr, "╔══════════════════════════════════════════════════════════════════╗")
+		fmt.Fprintln(os.Stderr, "║  ❌ PR CREATION BLOCKED                                          ║")
+		fmt.Fprintln(os.Stderr, "╠══════════════════════════════════════════════════════════════════╣")
+		fmt.Fprintln(os.Stderr, "║  Gas Town workers push directly to main. PRs are forbidden.     ║")
+		fmt.Fprintln(os.Stderr, "║                                                                  ║")
+		fmt.Fprintln(os.Stderr, "║  Instead of:  gh pr create ...                                   ║")
+		fmt.Fprintln(os.Stderr, "║  Do this:     git push origin main                               ║")
+		fmt.Fprintln(os.Stderr, "║                                                                  ║")
+		fmt.Fprintln(os.Stderr, "║  Why? PRs add friction that breaks autonomous execution.        ║")
+		fmt.Fprintln(os.Stderr, "║  See: ~/gt/docs/PRIMING.md (GUPP principle)                     ║")
+		fmt.Fprintln(os.Stderr, "╚══════════════════════════════════════════════════════════════════╝")
+		fmt.Fprintln(os.Stderr, "")
+		os.Exit(2) // Exit 2 = BLOCK in Claude Code hooks
+
+	case "feature-branch":
+		fmt.Fprintln(os.Stderr, "")
+		fmt.Fprintln(os.Stderr, "╔══════════════════════════════════════════════════════════════════╗")
+		fmt.Fprintln(os.Stderr, "║  ⚠️  FEATURE BRANCH BLOCKED                                      ║")
+		fmt.Fprintln(os.Stderr, "╠══════════════════════════════════════════════════════════════════╣")
+		fmt.Fprintln(os.Stderr, "║  Gas Town workers commit directly to main. No feature branches. ║")
+		fmt.Fprintln(os.Stderr, "║                                                                  ║")
+		fmt.Fprintln(os.Stderr, "║  Instead of:  git checkout -b feature/...                        ║")
+		fmt.Fprintln(os.Stderr, "║  Do this:     git add . && git commit && git push origin main   ║")
+		fmt.Fprintln(os.Stderr, "║                                                                  ║")
+		fmt.Fprintln(os.Stderr, "║  Why? Feature branches lead to PRs. We push directly to main.  ║")
+		fmt.Fprintln(os.Stderr, "╚══════════════════════════════════════════════════════════════════╝")
+		fmt.Fprintln(os.Stderr, "")
+		os.Exit(2)
+
+	default:
+		// Unknown reason but we're in Gas Town context - block conservatively
+		fmt.Fprintf(os.Stderr, "❌ Operation blocked by Gas Town policy (reason: %s)\n", blockPRReason)
+		fmt.Fprintln(os.Stderr, "Gas Town workers push directly to main. See ~/gt/docs/PRIMING.md")
+		os.Exit(2)
+	}
+
+	return nil
+}