tests/PLAN.md: assert on bar/prompt/receipt via grid renderer (current design)

Author: capocasa

tests/PLAN.md

@@ -233,11 +233,15 @@ Two pieces:
 
 2. **Pty harness** — Nim has no stdlib pty; shell out to `script` on
    macOS / Linux: `script -q /dev/null ./3code -m stub.test "say hi"`
-   captures stdout while presenting a pty. Capture bytes, assert:
-   - `●` (the bullet) appears
-   - the canned reply text appears
-   - a dim token-receipt line (`○` + `↑↻↓` glyphs) appears
-   - the order is bullet → content → receipt
+   captures stdout while presenting a pty. Capture bytes, feed
+   through the same ANSI grid renderer used by `tests/test_footer.nim`,
+   assert on cell content:
+   - `●` (the bullet) appears on a content row
+   - the canned reply text appears below the bullet
+   - the token bar (cyan + bright, `↑↻↓` glyphs at column 2) is
+     visible after stream end with the prompt `❯ ` directly below
+   - on a *second* prompt, the previous turn's bar shows up as a
+     dim receipt flush against the LLM content (no permanent gap)
 
 ### Gotchas