fix: critical issues in wisp hook system

Code review fixes:

1. CRITICAL: Move polecat check to start of runSling
   - Previously wrote wisp THEN failed, leaving orphan
   - Now fails fast before any file operations

2. CRITICAL: Sanitize slashes in agent IDs for filenames
   - Agent IDs like 'gastown/crew/joe' were creating subdirs
   - Now converts '/' to '--' for safe filenames
   - Added sanitizeAgentID/unsanitizeAgentID helpers

3. MODERATE: Use git root instead of WorkDir in prime.go
   - Hooks are written to clone root, not cwd
   - Added getGitRoot() helper for consistency

4. MODERATE: Fix silent error swallowing
   - Now logs non-ErrNoHook errors when reading hooks
   - Warns if bead doesn't exist before burning hook
   - Preserves hook if bead is missing for debugging

internal/wisp/types.go

@@ -9,6 +9,7 @@
 package wisp
 
 import (
+	"strings"
 	"time"
 )
 
@@ -126,6 +127,23 @@ func NewPatrolCycle(formula, createdBy string) *PatrolCycle {
 }
 
 // HookFilename returns the filename for an agent's hook file.
+// Agent IDs containing slashes (e.g., "gastown/crew/joe") are sanitized
+// by replacing "/" with "--" to create valid filenames.
 func HookFilename(agent string) string {
-	return HookPrefix + agent + HookSuffix
+	// Sanitize agent ID: replace path separators with double-dash
+	// This is reversible and avoids creating subdirectories
+	sanitized := sanitizeAgentID(agent)
+	return HookPrefix + sanitized + HookSuffix
+}
+
+// sanitizeAgentID converts an agent ID to a safe filename component.
+// "gastown/crew/joe" -> "gastown--crew--joe"
+func sanitizeAgentID(agent string) string {
+	return strings.ReplaceAll(agent, "/", "--")
+}
+
+// unsanitizeAgentID converts a sanitized filename back to an agent ID.
+// "gastown--crew--joe" -> "gastown/crew/joe"
+func unsanitizeAgentID(sanitized string) string {
+	return strings.ReplaceAll(sanitized, "--", "/")
 }