fix(sling): accept bead IDs directly even when routing fails

When routing-based verification (verifyBeadExists) fails due to
routes.jsonl configuration issues, gt sling now falls back to pattern
matching via looksLikeBeadID to accept valid bead ID formats.

The fix ensures:
1. verifyBeadExists is tried first (routing-based lookup)
2. verifyFormulaExists is tried second (formula check)
3. looksLikeBeadID pattern match is used as final fallback

Also improved looksLikeBeadID to accept any 1-5 letter lowercase
prefix followed by hyphen and alphanumeric chars.

Fixes: gt sling bd-xxx failing with "not a valid bead or formula"
when the bead exists but routing cannot find it.

Closes: gt-9e8s5

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

internal/cmd/sling.go

@@ -210,16 +210,23 @@ func runSling(cmd *cobra.Command, args []string) error {
 
 		// Try as bead first
 		if err := verifyBeadExists(firstArg); err == nil {
-			// It's a bead
+			// It's a verified bead
 			beadID = firstArg
 		} else {
-			// Not a bead - try as standalone formula
+			// Not a verified bead - try as standalone formula
 			if err := verifyFormulaExists(firstArg); err == nil {
 				// Standalone formula mode: gt sling <formula> [target]
 				return runSlingFormula(args)
 			}
-			// Neither bead nor formula
-			return fmt.Errorf("'%s' is not a valid bead or formula", firstArg)
+			// Not a formula either - check if it looks like a bead ID (routing issue workaround).
+			// Accept it and let the actual bd update fail later if the bead doesn't exist.
+			// This fixes: gt sling bd-ka761 beads/crew/dave failing with 'not a valid bead or formula'
+			if looksLikeBeadID(firstArg) {
+				beadID = firstArg
+			} else {
+				// Neither bead nor formula
+				return fmt.Errorf("'%s' is not a valid bead or formula", firstArg)
+			}
 		}
 	}