fix(rag): stop the per-run blocks from folding — the container is the one disclosure

The owner refinement (2026-10-06): the per-run thinking and tool-call
blocks inside the Reasoning bubble were individually collapsible
details elements — a fold inside the fold. A tool frame closed the
previous thinking block, so the visible thinking vanished mid-turn;
and the pinned-tail follow died on the append of every run after the
first (the pin was captured AFTER the new block's height growth
contaminated the 32px reading).

- app.js: the in-container runs are now plain divs —
  createThinkingRunEl (div.thinking + static .thinking-summary label +
  .thinking-text) and createToolRunEl (div.tool-calls-disclosure +
  static .tool-calls-summary label + the .tool-calls list); they never
  open or fold (the container is the ONE open/fold control, open
  through the turn, folded at settle — unchanged); the pin capture
  moves BEFORE ensureThinkingRun/ensureToolRun append (plus the
  first-frame edge: no container yet -> always pinned);
  closeCurrentRun just ends the run; closeAllRuns stays the defensive
  legacy guard; restoreTimeline/addSegments (shared.js) use the div
  builders; the legacy no-segments restore path keeps the old
  details-based blocks byte-identical
- styles.css: the in-container runs are distinct by label + rail
  (brand-ink Thinking label on a brand-soft rail; accent-ink
  Tool call(s) (N) label on a neutral rail); the interactive
  treatment (cursor + chevron) is scoped to the legacy <summary>; the
  inner windows stay disabled (the container's .reasoning-body is the
  ONE live scroll surface)
- unit + E2E: the D5-refinement contract is pinned — one
  details.reasoning disclosure, per-run blocks as plain divs, zero
  nested <details> inside the container, the container as the only
  open/fold control, the .reasoning-body window auto-follows the
  tail while streaming

unit+integration 3738 passed (coverage 99%), ruff + pyright clean, all
five affected E2E suites pass in isolation (reasoning_bubble 6,
thinking_timeline 6, thinking_display 5, thinking_scroll 8,
tool_call_compact 4), verified live: the follow holds through a long
thinking stream, the tool-frame transition, and the second thinking
run; restore renders the div structure without client-side errors

LLM-Generated: true

tests/unit/test_frontend_tool_states.py

@@ -300,8 +300,18 @@ def test_segments_keep_arrival_order_above_the_bubble() -> None:
     )
     assert "??" not in t, ("the old anchor chain is GONE — the container "
         "append is the only anchor")
-    assert "block.open = true" in t
-    assert "disc.open = true" in d
+    assert "createThinkingRunEl()" in t, (
+        "D5 refinement: a plain div — never collapsible"
+    )
+    assert "createToolRunEl()" in d, (
+        "D5 refinement: a plain div — never collapsible"
+    )
+    assert ".open =" not in t, (
+        "D5 refinement: the in-container runs are non-collapsible divs"
+    )
+    assert ".open =" not in d, (
+        "D5 refinement: the in-container runs are non-collapsible divs"
+    )
 
 
 def test_tool_call_style_is_accent_and_contrast_safe() -> None: