polish(v0.5.3): v0.4 lease-prompt hint, invocation-name in user-facing commands, smoke-checklist fixes

Three independent v0.5.3 polish items surfaced during manual WSL smoke testing,
bundled into one commit since they're all string/UX touches with no behavior change.

1. v0.4 lease-prompt tightening (`internal/session/{lease,run,run_preflight}.go`,
   `cmd/entry.go`): when ctask is about to enter direct mode on a workspace that
   already has a live tmux session, the "Continue anyway?" prompt now suggests
   `ctask attach <slug>` as the reattach path. Threaded via
   `PreflightOpts.ActiveLeaseHint` / `LaunchOpts.ActiveLeaseHint`; computed in
   `cmd/entry.go::directModeTmuxHint` (best-effort: silent when no tmux on PATH
   or no session for the workspace). Closes the footgun where a user forgot to
   `export CTASK_SESSION_MODE=persistent` in a second terminal and hit the v0.4
   coexistence prompt without realizing tmux passive-reattach was the intended
   path.

2. Invocation-name in user-facing command hints (`cmd/invocation.go` new,
   `cmd/{persistent,entry,resume,doctor}.go`): the binary name printed in
   bypass / restore / "create one with" suggestions now reflects
   `filepath.Base(os.Args[0])` instead of a hard-coded "ctask". Local-build
   PowerShell users running `.\ctask.exe` see `ctask.exe new <ws> --direct`,
   matching what they need to type. Installed contexts continue to see `ctask`.
   Test seam (`invocationNameOverride`) pins the name to "ctask" in unit tests
   so substring assertions stay stable across Go test binary names. Descriptive
   prose ("ctask persistent mode requires...") and the ssh-remote hint
   (`ssh -t <host> ctask <subcmd>`) intentionally keep the literal "ctask" —
   they refer to the program identity / remote invocation, not the local
   command form. Affected tests: `cmd/{persistent,resume}_test.go` tightened to
   check the full `"<binary> <subcmd> <workspace> --direct"` form.

3. Smoke-checklist fixes (`docs/.../2026-05-08-v0.5.3-smoke-test-checklist.md`):
   six issues caught during the run -- S2 now exports CTASK_SESSION_MODE in
   both terminals (previously only WSL-A had it, which routed WSL-B's
   secondary resume through direct mode instead of passive reattach); O3/A2
   tmux-ls expectations corrected (tmux doesn't emit a literal "(detached)"
   token); P2 expected behavior rewritten (passive reattach detach returns to
   prompt immediately -- AttachExisting calls only shell.AttachSession with
   no PollSessionEnd, the owner is responsible for finalize); A1 no longer
   asks for Ctrl-C in WSL-B; A6 path now uses a glob (was hardcoded to the
   checklist's authoring date, broke on v0.5.1 local-time directory naming);
   M1 PATH-hide rewritten to `$HOME/.local/bin` only (was `:/bin` which is a
   symlink to /usr/bin on usrmerge systems, did not hide tmux) and uses
   `command -v` instead of `which` (which is itself in /usr/bin, unreachable
   under the minimal PATH); M3/M4 reordered so the no-workspace verification
   runs after PATH is restored (was silently failing under minimal PATH);
   T1 wording made "substring match" explicit; T2 wording made N/A
   unambiguous; section 10 split into 10a-10f, each a separate input, to
   work around PSReadLine multi-line paste parsing.

cmd/persistent_test.go

@@ -22,6 +22,18 @@ func withTTYCheck(t *testing.T, fn func() bool) {
 	t.Cleanup(func() { isTTYCheck = orig })
 }
 
+// withInvocationName pins the binary name surfaced in user-facing hints
+// to a fixed value (typically "ctask") for the duration of the test, so
+// substring assertions against rendered hints stay stable regardless of
+// the Go test binary's name. Must NOT run in parallel — mutates a
+// package global.
+func withInvocationName(t *testing.T, name string) {
+	t.Helper()
+	orig := invocationNameOverride
+	invocationNameOverride = name
+	t.Cleanup(func() { invocationNameOverride = orig })
+}
+
 func TestPreflightRefusesNativeWindows(t *testing.T) {
 	if runtime.GOOS != "windows" {
 		t.Skip("native-Windows refusal applies only on Windows")
@@ -64,6 +76,7 @@ func TestPreflightRefusesNonTTY(t *testing.T) {
 	}
 	os.Unsetenv("TMUX")
 	withTTYCheck(t, func() bool { return false })
+	withInvocationName(t, "ctask")
 	_, err := preflightPersistentEntry("resume")
 	if err == nil {
 		t.Fatal("expected refusal when not a TTY")
@@ -74,8 +87,8 @@ func TestPreflightRefusesNonTTY(t *testing.T) {
 	if !strings.Contains(err.Error(), "ssh -t") {
 		t.Errorf("error should mention ssh -t: %v", err)
 	}
-	if !strings.Contains(err.Error(), "ctask resume") {
-		t.Errorf("error should mention command-specific bypass: %v", err)
+	if !strings.Contains(err.Error(), "ctask resume <workspace> --direct") {
+		t.Errorf("error should mention command-specific bypass form: %v", err)
 	}
 }
 
@@ -85,9 +98,10 @@ func TestPreflightCommandNameRendersInHints(t *testing.T) {
 	}
 	os.Unsetenv("TMUX")
 	withTTYCheck(t, func() bool { return false })
+	withInvocationName(t, "ctask")
 	_, err := preflightPersistentEntry("attach")
-	if err == nil || !strings.Contains(err.Error(), "ctask attach") {
-		t.Errorf("commandName must appear in hint: %v", err)
+	if err == nil || !strings.Contains(err.Error(), "ctask attach <workspace> --direct") {
+		t.Errorf("commandName must appear in bypass hint: %v", err)
 	}
 }