feat(chat): stream model thinking over SSE and show it in a collapsible block

tests/unit/test_frontend_feedback.py

@@ -91,3 +91,101 @@ def test_busy_button_style_tokens() -> None:
     assert re.search(r"\.spinner \{[^}]*width: 16px", css)
     assert "Thinking…" in js
     assert 'sendLabel.textContent' in js
+
+
+# ---------- thinking display (phase 17) ----------
+
+
+def test_thinking_event_is_a_first_class_turn_branch() -> None:
+    """Phase 17: `thinking` SSE frames stream live into the collapsible
+    Thinking block — the typing dots make way, the 120s pre-token guard
+    clears (the stream is alive), and the text renders through the
+    escape-first markdown renderer (XSS-safe). While open, the stream is
+    pinned to the bottom of the block."""
+    js = _js()
+    thinking_idx = js.find('ev.type === "thinking"')
+    delta_idx = js.find('ev.type === "delta"')
+    assert -1 < thinking_idx < delta_idx, "the turn handler must branch on thinking frames"
+    branch = js[thinking_idx:delta_idx]
+    assert "thinkingAcc += ev.text" in branch
+    assert "sawThinking = true" in branch
+    assert "clearTurnTimeout()" in branch, "first thinking frame clears the 120s guard"
+    assert "removeTyping()" in branch, "the live block replaces the typing dots"
+    assert "ensureThinkingBlock(wrap)" in branch
+    assert "renderMarkdown(thinkingAcc)" in branch, "escape-first renderer (XSS-safe)"
+    assert "textEl.scrollTop = textEl.scrollHeight" in branch, "bottom-pinned while open"
+
+
+def test_thinking_block_helpers_are_idempotent() -> None:
+    """ensureThinkingBlock returns the existing `.thinking` details or
+    creates it OPEN above the .bubble; closeThinkingBlock is a no-op
+    without a block and never reopens one once the answer started."""
+    js = _js()
+    fn = js.find("function ensureThinkingBlock")
+    assert fn != -1, "ensureThinkingBlock must exist (near addTyping/removeTyping)"
+    body = js[fn : js.find("\n}\n", fn)]
+    assert "block.open = true" in body, "created open — the stream is the show"
+    assert "insertBefore" in body
+    assert 'querySelector(".bubble")' in body, "the block sits ABOVE the bubble"
+    fn2 = js.find("function closeThinkingBlock")
+    assert fn2 != -1, "closeThinkingBlock must exist"
+    body2 = js[fn2 : js.find("\n}\n", fn2)]
+    assert "block.open = false" in body2
+
+
+def test_delta_branch_collapses_block_and_transitions_to_streaming() -> None:
+    """The first answer delta transitions thinking → streaming (even when
+    thinking created the wrap first) and auto-collapses the block —
+    idempotent, and it never reopens once the answer started."""
+    js = _js()
+    delta_idx = js.find('ev.type === "delta"')
+    done_idx = js.find('ev.type === "done"')
+    assert -1 < delta_idx < done_idx
+    branch = js[delta_idx:done_idx]
+    assert "uiState === UI_STATE.thinking" in branch
+    assert "setUiState(UI_STATE.streaming)" in branch
+    assert "closeThinkingBlock(wrap)" in branch
+
+
+def test_done_branch_sets_sawdone_and_closes_block() -> None:
+    """On `done` the turn marks itself complete (sawDone — the stream-drop
+    guard keys off it) and settles the thinking block closed."""
+    js = _js()
+    done_idx = js.find('ev.type === "done"')
+    error_idx = js.find('ev.type === "error"')
+    assert -1 < done_idx < error_idx
+    branch = js[done_idx:error_idx]
+    assert "sawDone = true" in branch
+    assert "closeThinkingBlock(wrap)" in branch
+
+
+def test_stream_drop_guard_reports_severed_stream() -> None:
+    """A stream that delivered frames but no `done` event ends in the error
+    state (never a silent idle with a half bubble); the zero-frame case
+    falls through to the existing empty-answer fallback. The guard runs
+    after readSSE, before that fallback."""
+    js = _js()
+    assert "let sawDone = false" in js
+    assert re.search(r"if \(!sawDone && !aborted && \(acc \|\| thinkingAcc\)\)", js), (
+        "sawDone stream-drop guard missing after readSSE"
+    )
+    assert "The stream ended before my answer finished" in js
+    sse_idx = js.find("await readSSE(res,")
+    guard_idx = js.find("!sawDone && !aborted")
+    fallback_idx = js.find("!aborted && !wrap")
+    assert -1 < sse_idx < guard_idx < fallback_idx, (
+        "guard must sit between readSSE and the zero-frame fallback"
+    )
+
+
+def test_thinking_chevron_stills_under_reduced_motion() -> None:
+    """Phase 17: the only motion in the thinking block (the summary
+    chevron rotation) is disabled under prefers-reduced-motion."""
+    css = _css()
+    blocks = re.findall(
+        r"@media \(prefers-reduced-motion: reduce\) \{([\s\S]*?)\n\}", css
+    )
+    assert any(
+        "details.thinking summary::before" in b and "transition: none" in b
+        for b in blocks
+    ), "chevron transition must still under reduced motion"