feat(v0.6): info source attribution on Agent and Launch session mode

Adds source-attribution rendering to `ctask info` for the two Phase 1
settings whose effective value depends on user-level defaults: the
agent recorded in task.yaml and the configured launch session mode.

cmd/info.go:

- runInfo loads the resolver once (config.LoadResolver) and reuses
  it across the rendering — matches the user's correction that "new
  doctor/info code should load the resolver once and reuse it".
- Agent line now reads `Agent: <value> (workspace)` when task.yaml
  has a non-empty agent (the common case), or `Agent: <value>
  (default)` / `Agent: <value> (default — <source label>)` when the
  field is empty and the value comes from the resolver fallback
  chain. The fallback path is informational only: every workspace
  created by recent ctask versions writes the resolved default into
  task.yaml at Create time, so the (workspace) branch is what users
  normally see.
- New "Launch session mode:" line lives immediately after Agent and
  before Created — outside the v0.5.4 Session block per the user's
  placement decision ("Keep it outside the Session block because it
  represents the configured launch default, not the current session
  lease mode"). Format: `Launch session mode: <value> (<source>)`.
- Two small helpers added: agentLineWithSource composes the agent
  payload + label; infoSourceLabel renders a single-row source
  string (CTASK_X env var / config file / built-in default /
  platform override). infoSourceLabel intentionally omits the
  override-chain suffix used by doctor — info's row layout has no
  room for the extra parenthetical.

cmd/info_attribution_test.go (5 cases):

- TestInfoAgentSourceWorkspace — task.yaml with agent set → "(workspace)"
- TestInfoAgentSourceDefaultForLegacy — empty agent → "(default)"
- TestInfoLaunchSessionModeFromConfig — config session_mode value +
  "config file" source label
- TestInfoLaunchSessionModeBuiltinDefault — no config, no env →
  "direct (built-in default)"
- TestInfoLaunchSessionModeAfterAgentBeforeCreated — placement check:
  Agent < Launch session mode < Created in the rendered output

Smoke-verified against an existing v0.5.x workspace on the installed
binary; render order and source labels match the spec example.

cmd/info.go

@@ -32,12 +32,20 @@ func runInfo(cmd *cobra.Command, args []string) error {
 	ws := resolveOne(roots, args[0], true)
 	m := ws.Meta
 
+	// v0.6: load the resolver once and reuse it across this info
+	// invocation. The Agent line gains a workspace-vs-default source
+	// label; a new Launch session mode line surfaces the configured
+	// launch default with its own source attribution.
+	resolver := config.LoadResolver()
+
 	fmt.Printf("Task:      %s\n", m.Slug)
 	fmt.Printf("Title:     %s\n", m.Title)
 	fmt.Printf("Category:  %s\n", m.Category)
 	fmt.Printf("Status:    %s\n", m.Status)
 	fmt.Printf("Mode:      %s\n", m.Mode)
-	fmt.Printf("Agent:     %s\n", m.Agent)
+	fmt.Printf("Agent:     %s\n", agentLineWithSource(m.Agent, resolver))
+	fmt.Printf("Launch session mode: %s (%s)\n",
+		resolver.SessionMode().Value, infoSourceLabel(resolver.SessionMode()))
 	// v0.5.1: display timestamps in local time. task.yaml stores UTC;
 	// info converts for friendliness so the shown time matches the user's
 	// wall clock.
@@ -85,6 +93,48 @@ func runInfo(cmd *cobra.Command, args []string) error {
 	return nil
 }
 
+// agentLineWithSource builds the value portion of info's Agent line
+// with v0.6 source attribution. When task.yaml has a non-empty agent
+// field, that value is workspace state and surfaces as
+// "<value> (workspace)". When the field is empty (legacy or
+// hand-crafted task.yaml), the line falls through to the user-level
+// default chain and is labelled "<value> (default)" plus the source
+// when the default did NOT come from the built-in.
+//
+// The fallback path is informational only: ctask new always writes
+// the resolved default into task.yaml, so the legacy branch never
+// fires for workspaces created by recent versions.
+func agentLineWithSource(workspaceAgent string, r *config.Resolver) string {
+	if workspaceAgent != "" {
+		return workspaceAgent + " (workspace)"
+	}
+	s := r.DefaultAgent()
+	if s.Source == config.Builtin {
+		return s.Value + " (default)"
+	}
+	return fmt.Sprintf("%s (default — %s)", s.Value, infoSourceLabel(s))
+}
+
+// infoSourceLabel renders a setting's source for info output. Mirrors
+// formatSettingSource in doctor.go but without the override-chain
+// suffix; info lines are single-row and cannot fit the extra "(...)"
+// payload cleanly. Env-var sources surface their CTASK_X env-var name
+// (more specific than the bare "env var" label) so the user can spot
+// which shell variable to inspect.
+func infoSourceLabel(s config.ResolvedSetting) string {
+	switch s.Source {
+	case config.EnvVar:
+		if s.EnvName != "" {
+			return s.EnvName + " env var"
+		}
+		return "env var"
+	case config.PlatformOverride:
+		return "platform override"
+	default:
+		return s.Source.String()
+	}
+}
+
 // printSessionBlock renders the v0.5.4 Session block for `ctask info`.
 //
 // Layout (values align at column 14 across the block):