Function stubBGCommand

internal/app/background_test.go:103–128

stubBGCommand swaps claude.BGCommandRunner with a recorder that dispatches on args: `agents` returns *agentsJSON (mutable so a test can change registry state mid-run), `--resume` returns resumeBanner, the rest are spawns (returning spawnBanner). Both banners default to bgBanner; tests set resumeBann

(t *testing.T, agentsJSON *string)

// bgBanner; tests set resumeBanner to simulate the new id --bg mints on
// resume.
func stubBGCommand(t *testing.T, agentsJSON *string) *bgCalls {
	t.Helper()
	c := &bgCalls{spawnBanner: bgBanner, resumeBanner: bgBanner}
	old := claude.BGCommandRunner
	claude.BGCommandRunner = func(workDir string, args []string) ([]byte, error) {
		if len(args) >= 1 && args[0] == "agents" {
			c.agents++
			return []byte(*agentsJSON), nil
		}
		for _, a := range args {
			if a == "--resume" {
				c.resume++
				c.lastResume = args
				if c.onResume != nil {
					c.onResume()
				}
				return []byte(c.resumeBanner), nil
			}
		}
		c.spawn++
		c.lastSpawn = args
		return []byte(c.spawnBanner), nil
	}
	t.Cleanup(func() { claude.BGCommandRunner = old })
	return c
}

// TestCmdDoBackgroundFreshSpawn: $FLOW_TERM=bg flow do <task> spawns a bg
// agent, captures the REAL full session id (not a pre-allocated phantom),