brain-of-reese/.agent/phases/complete/21_thinking_no_scroll/00_phase.md

Phase 21 — Thinking Window: No Scroll Back, Just Live

Source: TODO.md L4 — "Disable scroll in the thinking window. Users don't need to scroll back through thinking, just see it live." Story: .agent/user_stories/thinking-no-scroll.md (created by task 02) Context: frontend/assets/styles.css — details.thinking .thinking-text (today: max-height: 320px; overflow-y: auto;, i.e. a user-scrollable 320px window, ~line 444); frontend/assets/app.js — the phase-17 thinking block (ensureThinkingBlock, the streaming thinking branch that appends chunks and already pins the stream to the bottom: textEl.scrollTop = textEl.scrollHeight, ~line 886), and the phase-14 restore path (stored thinking re-renders a collapsed block).

Objective

The live Thinking block is a scratchpad, not a transcript. The user must not be able to scroll back through it — the 320px window always shows the live tail of the reasoning stream (the existing per-chunk bottom-pinning stays). Wheel, drag, and keyboard scrolling on .thinking-text stop working; the stream itself keeps pinning to the bottom as chunks arrive.

Owner-confirmed (2026-08-24, roadmap A2)

1. Keep the 320px clip — "just see it live" means the window stays a fixed 320px viewport showing the newest lines; no auto-height growth, no "↓ more" affordance.
2. The answer bubble is untouched — final answers keep their existing scroll behavior (phase 11 long answers).
3. Restored (collapsed) Thinking blocks are untouched — the phase-14 restore renders them collapsed, where overflow is moot.

Design

• CSS (the whole functional change): details.thinking .thinking-text — overflow-y: auto → overflow-y: hidden; keep max-height: 320px. overflow: hidden still permits programmatic scrolling (scrollTop), so the phase-17 pin (textEl.scrollTop = textEl.scrollHeight on every thinking chunk) keeps the window glued to the live tail — no JS change needed. Add a CSS comment: no user scroll back (owner choice 2026-08-24): the window is a live tail only — the JS bottom-pin is the sole scroller.
• No JS change — the pin already exists; nothing else touches .thinking-text scroll.
• Non-goals: no change to the answer bubble, the collapsed restore state, the summary/chevron, or the auto-collapse on first delta (phase 17).

Dependencies

• 17_thinking_display (complete) — the block, the pin, the restore.
• 18_follow_bottom_scroll (complete) — no overlap (chat-page scroll gate only; the thinking window is a separate inner element).
• 11_long_answers (complete) — the untouched answer-bubble behavior.

Tasks

1. 01_disable_thinking_scroll.md — the CSS change + source-level unit pins.
2. 02_e2e_story_suite_commit.md — tests/e2e/test_thinking_no_scroll.py (the story gate, isolated), regression suites, story file, final validation, the single atomic commit, phase move to complete/.

Locked decisions

• A11 untouched — no CDN, pure CSS. A16 honored — one new story E2E suite + adapted regressions. No anchor changed.

Testing & Quality

• Unit (source-level, new tests/unit/test_thinking_no_scroll.py, repo source-pin pattern): styles.css carries details.thinking .thinking-text with overflow-y: hidden and max-height: 320px; the phase-17 pin line (textEl.scrollTop = textEl.scrollHeight) still present in app.js (the live-tail mechanism must not be lost).
• Integration: none (no app/ changes).
• Coverage: frontend-only; the >90% app/ gate is unaffected.
• E2E: tests/e2e/test_thinking_no_scroll.py (task 02), green in isolation (prereq podman compose up -d db).
• Lint/types: uv run ruff check . && uv run pyright clean.

Completion Criteria

• With a long thinking stream, wheel/mouse-drag/keyboard on .thinking-text do not move it; the visible content is always the live tail (scrollTop === scrollHeight after each chunk, within 1px).
• Computed style: overflow-y: hidden, max-height: 320px.
• A long answer bubble still scrolls normally; a restored collapsed Thinking block still renders (phase 17 regression).
• uv run pytest green; uv run pytest --cov=app --cov-report=term-missing ≥ today's number.
• uv run pytest tests/e2e/test_thinking_no_scroll.py -v --no-cov green in isolation; regressions green in isolation: test_thinking_display.py, test_long_answers.py.
• uv run ruff check . && uv run pyright clean.
• UI Structure Check (AGENTS.md rule 5): no new surface; the block keeps its focus-visible summary, aria contract, and reduced-motion behavior.
• .agent/user_stories/thinking-no-scroll.md exists.
• One --no-gpg-sign commit (below); .agent/phases/todo/21_thinking_no_scroll/ moved to .agent/phases/complete/.

Commit

git add -A .agent/ frontend/ tests/ && git commit --no-gpg-sign -m "fix(ui): thinking window no longer scrolls — live 320px view pinned to the stream tail"