fix(tui): coalesce thinking deltas on \n (v0.7.1)

Operator: "thinking tokens seem to be split by token — each on a
newline, is that correct? We don't want that."

Root cause: v0.6.5 wrote each Thinking SSE delta as its own
`thinking_log.write(event.content)` call. Worldtree emits Thinking
events at token granularity (per-token or per-few-tokens), so EACH
token became its own RichLog line — visually choppy, one short
fragment per visual row. Wrong UX.

## Fix: coalesce-on-newline

Thinking deltas accumulate in `TuiPresenterState.thinking_chunk_buffer`
(new str field). On each Thinking event:

  1. Append delta content to buffer.
  2. Flush every COMPLETE line (chars before each `\n`) as one
     thinking_log.write(line) call.
  3. Leave the post-final-`\n` tail in the buffer for the next delta.

On any non-thinking event (run close):
  1. Flush remaining buffer tail (if any) as one final line.
  2. Write Rule(end).

Empty lines (blank paragraph separators in the model's `\n\n` flow)
are skipped — they'd render as no-content RichLog entries which
just add vertical noise. Natural paragraph breaks become single
visible lines; multi-paragraph thinking renders top-to-bottom.

## Verified live (tier-3 smoke against personal Worldtree)

Defined a `thinky-smoke` agent via `python -m ratatoskr.tier3 define`,
asked "What is 12 times 13?". Thinking pane rendered with natural
paragraph chunks:

  ── turn N · thinking #1 start ──
  Thinking Process:
  1.  **Analyze the Request:** The user wants to know the result of $12 \times 13$.
  2.  **Calculate:**
      *   Method 1: Standard multiplication.
          $$12 \times 10 = 120$$
          $$12 \times 3 = 36$$
          $$120 + 36 = 156$$
      *   Method 2: $(10 + 2)(10 + 3) = 100 + 30 + 20 + 6 = 156$.
  ── turn N · thinking #1 end ──

Each line = one natural paragraph or list item. No per-token fragments.

## Edge cases noted

- Long-running thinking with NO `\n` at all stays buffered until run
  close → operator sees nothing until close. Possible follow-up: add
  a length-threshold flush (e.g., > 500 chars → flush at the last
  space). For now this is acceptable; thinking content typically has
  `\n` breaks every few sentences.
- Empty deltas (`""`) are ignored implicitly — no buffer growth, no
  flush.
- `\n` at the very start of a delta flushes whatever was buffered
  before, then leaves the empty post-`\n` tail (empty string) in the
  buffer, which doesn't show up as an empty line because of the
  `if line:` guard.

## Contract amendment

docs/contracts/issues/13.contract.md INV-022 amended for v0.7.1
coalesce semantics. Drift-check clean.

## Tests

265/265 GREEN; ruff clean. Two updated tests:

- `test_thinking_streams_into_thinking_log` → renamed
  `test_thinking_coalesces_until_newline`: 3 token-shaped deltas
  with no `\n` → only Rule(start) writes, buffer holds accumulated.
- NEW `test_thinking_flushes_on_newline`: delta carrying `\n` →
  Rule(start) + accumulated line + clear buffer.
- `test_thinking_closes_to_thinking_log`: 2 deltas "a", "b" +
  close → Rule(start) + tail-flush "ab" + Rule(end) = 3 writes
  (was 4 with per-delta).

Patch bump (v0.7.0 → v0.7.1) — internal presenter routing change;
no public-API or layout change.

persistent-memory.md

@@ -32,9 +32,9 @@ separate dev team rather than an in-tree Worldtree tool.
 
 ## Current state / in-flight
 
-_As of 2026-05-25 (post-v0.7.0 Tier 3 agent lifecycle):_
+_As of 2026-05-25 (post-v0.7.1 thinking coalesce-by-newline):_
 
-**Status: v0.7.0 shipped.** Ten core features complete (`sse_client`
+**Status: v0.7.1 shipped.** Ten core features complete (`sse_client`
 #1, `sessions` #2, `cli` #3, `tui` #4, `--end-user-id` #5, TUI
 startup error visibility #6, presenter contract semantics amendment
 #12, startup agent picker #8, §5 layout reshape + Tools pane #13)
@@ -51,7 +51,8 @@ Static in the footer (static "Tools" v1; dynamic when more tabs
 land). CLI mode (--send) unaffected by design — INV-018.
 
 Last commits on `main`:
-- v0.7.0 feat(tier3): ratatoskr.tier3 module + CLI — Worldtree Tier 3 lifecycle
+- v0.7.1 fix(tui): coalesce thinking deltas on `\n` — no more per-token newlines
+- `c086ae2` feat(tier3): ratatoskr.tier3 module + CLI (v0.7.0)
 - `d356990` refactor(tui): thinking streams into thinking-log (v0.6.5)
 - `82437bd` style(tui): picker highlighted item → Aurora blue (v0.6.4)
 - `ac690c1` style(tui): restore Australis palette, only $background → pure black (v0.6.3)