fix(tui,sse): inline Text streaming + empty-id keepalive skip (v0.8.1)

Two related fixes for the same user-reported bug pattern from a
running session against ratatoskr:sindra (qwen3.6-35-a3b-heretic):

## 1. Streaming text overlapping the transcript

Operator: "new text comes at the bottom and overwrites the existing
pane information instead of pushing it up naturally."

Root cause: the v0.6.0 `#current-text` Static was `dock: bottom`
with `height: auto`, sitting between the transcript RichLog (1fr)
and the prompt Input (dock: bottom). As text streamed, the Static
grew UPWARD but Textual didn't dynamically resize the 1fr transcript
to accommodate — the growing Static visually OVERLAPPED the
transcript's bottom rows. On Done, `current_text.update("")` snapped
it to height 0 and the transcript re-laid-out — "boom, everything
updates."

Fix: remove `#current-text` Static entirely. Apply the same
coalesce-on-newline pattern v0.7.1 used for thinking — Text deltas
accumulate in `TuiPresenterState.text_chunk_buffer`, flushing whole
lines (each `\n` boundary) directly to `log` (transcript). On Done:
flush remaining tail, then [done] label + Rule + Markdown body.

Trade-off accepted: streamed lines + post-Done Markdown body are
both in the transcript (some content duplication). The Markdown
body re-renders the same content with proper formatting (lists,
bold, code blocks). Acceptable — operator gets both the live-progress
streaming AND the canonical rendered version.

## 2. MalformedSseId raw='' crashing every turn

Operator: "current session is erroring on every turn with
[malformed_sse_id] raw=''"

Worldtree's qwen3.6-35-a3b-heretic provider emits some events
without `id:` lines (observed 2026-05-25 mid-stream). When the FIRST
such event arrives before any prior id has been seen, httpx_sse's
`ServerSentEvent.id` is `""`. `_parse_sse_id('')` raised ValueError
→ MalformedSseId → turn worker bailed → operator saw the label
every turn.

Per SSE RFC, events without `id:` are legitimate (they just don't
update Last-Event-ID). Issue #7 already covered the empty-DATA
keepalive case with skip-silently semantics. Empty-id is the same
shape of wire weirdness; same fix shape:

  if sse.id == "":
      continue  # treat as keepalive

Ordered AFTER the empty-data branch so an empty-data + empty-id
event still gets skipped on the data check.

## Tests + smoke

287/287 GREEN (was 286, +1 for empty-id skip; +1 net Text-flow test
adjustments). Ruff clean.

Verified Worldtree alive when the user hit the empty-id bug
(/healthz returned ok in 18ms) — not a server-down issue, just
wire-format mid-stream.

## Caveats

The fix doesn't recover content from the dropped empty-id event.
If the event happened to carry meaningful data (not a true
keepalive), we silently lose it. Acceptable trade-off: pre-v0.8.1
EVERY turn died on the offending agent; post-v0.8.1 the turn
continues and any single dropped frame is recoverable from logs if
debugging. Worldtree-side fix (always emit ids) is the right
upstream answer; ratatoskr just stops panicking on wire weirdness.

Patch bump (v0.8.0 → v0.8.1) — both fixes are bug fixes; no public
API change. The `TuiPresenterState.render` signature loses the
`current_text` parameter (was added v0.6.0), but presenter is an
internal contract; no external callers.

tests/test_sse_client.py

@@ -711,6 +711,47 @@ def _sse_raw_chunk(sse_id: str, raw_data: str) -> bytes:
     return f"id: {sse_id}\ndata: {raw_data}\n\n".encode()
 
 
+def _sse_no_id_chunk(data: str) -> bytes:
+    """SSE frame with NO id line + arbitrary data (v0.8.1: keepalive shape)."""
+    return f"data: {data}\n\n".encode()
+
+
+class TestEmptyIdSkipped:
+    @respx.mock
+    async def test_empty_id_on_first_event_skipped(self) -> None:
+        """empty_id_on_first_event_skipped [v0.8.1]: stream starts with an
+        event carrying NO `id:` line → httpx_sse exposes sse.id == ''
+        (no prior id to inherit). Pre-v0.8.1: MalformedSseId raw='' crashed
+        the turn. v0.8.1: treat same as empty-data keepalive — skip silently.
+
+        Observed 2026-05-25 on Worldtree's qwen3.6-35-a3b-heretic provider:
+        the first stream frame had no id line, every turn died with
+        `[malformed_sse_id] raw=''`.
+        """
+        from ratatoskr.sse_client import Done as _Done
+        from ratatoskr.sse_client import Text as _Text
+
+        # First frame: no id line (httpx_sse → sse.id = ""). Skip it.
+        # Subsequent frames have ids; normal processing resumes.
+        stream = (
+            _sse_no_id_chunk('{"type":"keepalive"}')  # ← skipped (sse.id == "")
+            + _sse_chunk("42:1", {"type": "text", "content": "first"})
+            + _sse_chunk("42:2", _DONE_42_6)
+        )
+        respx.post("https://w.example/sessions/s1/messages").mock(
+            return_value=httpx.Response(
+                200, headers={"content-type": "text/event-stream"}, content=stream
+            )
+        )
+        async with httpx.AsyncClient(base_url="https://w.example") as client:
+            events = [e async for e in stream_turn(client, "s1", "hi")]
+        # 2 events — the no-id frame is invisible (no MalformedSseId crash).
+        assert len(events) == 2
+        assert isinstance(events[0], _Text)
+        assert events[0].content == "first"
+        assert isinstance(events[1], _Done)
+
+
 class TestEmptyDataSkipped:
     @respx.mock
     async def test_empty_data_skipped(self) -> None: