fix(lint): resolve all errcheck warnings

Fix ~50 errcheck warnings across the codebase:

- Add explicit `_ =` for intentionally ignored error returns (cleanup,
  best-effort operations, etc.)
- Use `defer func() { _ = ... }()` pattern for defer statements
- Handle tmux SetEnvironment, KillSession, SendKeysRaw returns
- Handle mail router.Send returns
- Handle os.RemoveAll, os.Rename in cleanup paths
- Handle rand.Read returns for ID generation
- Handle fmt.Fprint* returns when writing to io.Writer
- Fix for-select with single case to use for-range
- Handle cobra MarkFlagRequired returns

All tests pass. Code compiles without errors.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

internal/swarm/integration.go

@@ -37,9 +37,7 @@ func (m *Manager) CreateIntegrationBranch(swarmID string) error {
 	}
 
 	// Push to origin
-	if err := m.gitRun("push", "-u", "origin", branchName); err != nil {
-		// Non-fatal - may not have remote
-	}
+	_ = m.gitRun("push", "-u", "origin", branchName) // Non-fatal - may not have remote
 
 	return nil
 }
@@ -64,9 +62,7 @@ func (m *Manager) MergeToIntegration(swarmID, workerBranch string) error {
 	}
 
 	// Fetch the worker branch
-	if err := m.gitRun("fetch", "origin", workerBranch); err != nil {
-		// May not exist on remote, try local
-	}
+	_ = m.gitRun("fetch", "origin", workerBranch) // May not exist on remote, try local
 
 	// Attempt merge
 	err = m.gitRun("merge", "--no-ff", "-m",
@@ -102,7 +98,7 @@ func (m *Manager) LandToMain(swarmID string) error {
 	}
 
 	// Pull latest
-	m.gitRun("pull", "origin", swarm.TargetBranch) // Ignore errors
+	_ = m.gitRun("pull", "origin", swarm.TargetBranch) // Ignore errors
 
 	// Merge integration branch
 	err := m.gitRun("merge", "--no-ff", "-m",
@@ -138,15 +134,15 @@ func (m *Manager) CleanupBranches(swarmID string) error {
 	}
 
 	// Delete integration branch remotely
-	m.gitRun("push", "origin", "--delete", swarm.Integration) // Ignore errors
+	_ = m.gitRun("push", "origin", "--delete", swarm.Integration) // Ignore errors
 
 	// Delete worker branches
 	for _, task := range swarm.Tasks {
 		if task.Branch != "" {
 			// Local delete
-			m.gitRun("branch", "-D", task.Branch)
+			_ = m.gitRun("branch", "-D", task.Branch)
 			// Remote delete
-			m.gitRun("push", "origin", "--delete", task.Branch)
+			_ = m.gitRun("push", "origin", "--delete", task.Branch)
 		}
 	}
 

internal/swarm/landing.go

@@ -210,7 +210,7 @@ Manual intervention required.`,
 			swarmID, strings.Join(workers, "\n- ")),
 		Priority: mail.PriorityHigh,
 	}
-	router.Send(msg)
+	_ = router.Send(msg)
 }
 
 // notifyMayorLanded sends a landing report to Mayor.
@@ -233,5 +233,5 @@ Tasks merged: %d`,
 			result.BranchesCleaned,
 			len(swarm.Tasks)),
 	}
-	router.Send(msg)
+	_ = router.Send(msg)
 }

internal/swarm/manager_test.go

@@ -94,7 +94,7 @@ func TestManagerCancel(t *testing.T) {
 	m := NewManager(r)
 
 	swarm, _ := m.Create("epic-1", []string{"Toast"}, "main")
-	m.Start(swarm.ID)
+	_ = m.Start(swarm.ID)
 
 	if err := m.Cancel(swarm.ID, "user requested"); err != nil {
 		t.Errorf("Cancel failed: %v", err)
@@ -179,7 +179,7 @@ func TestManagerIsComplete(t *testing.T) {
 	}
 
 	// Complete the pending task
-	m.UpdateTaskState(swarm.ID, "task-1", TaskMerged)
+	_ = m.UpdateTaskState(swarm.ID, "task-1", TaskMerged)
 	complete, _ = m.IsComplete(swarm.ID)
 	if !complete {
 		t.Error("IsComplete should be true when all tasks merged")