fix(done): get issue ID from agent hook and detect integration branches (#411) (#453)

Branch names like "polecat/furiosa-mkb0vq9f" don't contain the actual
issue ID, causing gt done to incorrectly parse "furiosa-mkb0vq9f" as the
issue. This broke integration branch auto-detection since the wrong issue
was used for parent epic lookup.

Changes:
- After parsing branch name, check the agent's hook_bead field which
  contains the actual issue ID (e.g., "gt-845.1")
- Fix parseBranchName to not extract fake issue IDs from modern polecat branches
- Fix detectIntegrationBranch to traverse full parent chain (molecule → bug → epic)
- Include issue ID in polecat branch names when HookBead is set

Added tests covering:
- Agent hook returns correct issue ID
- Modern polecat branch format parsing
- Integration branch detection through parent chain

Fixes #411

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/done.go

@@ -215,6 +215,16 @@ func runDone(cmd *cobra.Command, args []string) error {
 		agentBeadID = getAgentBeadID(ctx)
 	}
 
+	// If issue ID not set by flag or branch name, try agent's hook_bead.
+	// This handles cases where branch name doesn't contain issue ID
+	// (e.g., "polecat/furiosa-mkb0vq9f" doesn't have the actual issue).
+	if issueID == "" && agentBeadID != "" {
+		bd := beads.New(beads.ResolveBeadsDir(cwd))
+		if hookIssue := getIssueFromAgentHook(bd, agentBeadID); hookIssue != "" {
+			issueID = hookIssue
+		}
+	}
+
 	// Get configured default branch for this rig
 	defaultBranch := "main" // fallback
 	if rigCfg, err := rig.LoadRigConfig(filepath.Join(townRoot, rigName)); err == nil && rigCfg.DefaultBranch != "" {
@@ -617,6 +627,21 @@ func updateAgentStateOnDone(cwd, townRoot, exitType, _ string) { // issueID unus
 	}
 }
 
+// getIssueFromAgentHook retrieves the issue ID from an agent's hook_bead field.
+// This is the authoritative source for what work a polecat is doing, since branch
+// names may not contain the issue ID (e.g., "polecat/furiosa-mkb0vq9f").
+// Returns empty string if agent doesn't exist or has no hook.
+func getIssueFromAgentHook(bd *beads.Beads, agentBeadID string) string {
+	if agentBeadID == "" {
+		return ""
+	}
+	agentBead, err := bd.Show(agentBeadID)
+	if err != nil {
+		return ""
+	}
+	return agentBead.HookBead
+}
+
 // getDispatcherFromBead retrieves the dispatcher agent ID from the bead's attachment fields.
 // Returns empty string if no dispatcher is recorded.
 func getDispatcherFromBead(cwd, issueID string) string {