brain-of-reese/tests/unit/test_frontend_scroll.py

"""Unit: the no-reply-autoscroll contract in the static frontend
(phase 42, owner direction 2026-08-27, TODO.md L5).

The owner removed the phase-18 follow-the-bottom auto-follow: the page
NEVER auto-scrolls while a turn streams (thinking / tool / delta frames
all leave the viewport alone), so a user reading earlier content is no
longer yanked down mid-answer. Scrolls happen only on explicit user
intent: the submit (the user's own message is revealed) and the phase-14
restore landing (one-shot, load-time).

The JS behavior itself is E2E-covered
(tests/e2e/test_no_reply_autoscroll.py); here we pin the source markers
of the new contract — the phase-18 gate is gone (no NEAR_BOTTOM_PX /
isNearBottom), scrollReveal scrolls unconditionally and is the single
scrollIntoView in app.js, addMessage takes an explicit `scroll` intent,
and the streaming handlers contain no page-scroll call at all — so a
silent regression back to per-frame autoscroll is caught without a
browser.
"""
from __future__ import annotations

import re
from pathlib import Path

FRONTEND = Path(__file__).resolve().parents[2] / "frontend"
APP_JS = FRONTEND / "assets" / "app.js"


def _js() -> str:
    return APP_JS.read_text(encoding="utf-8")


def _fn_body(js: str, name: str) -> str:
    """Source of the function starting at `function <name>` (to its closing
    brace at column 0) — same slicing style as test_frontend_feedback.py."""
    fn = js.find(f"function {name}")
    assert fn != -1, f"{name} must exist in app.js"
    return js[fn : js.find("\n}\n", fn)]


def test_phase18_gate_is_gone() -> None:
    """The follow-the-bottom machinery (phase 18) is removed by owner
    direction 2026-08-27: no band constant, no gate function, and no
    document-scroller measurement left anywhere in app.js."""
    js = _js()
    assert "NEAR_BOTTOM_PX" not in js, "the 200px band constant must be gone"
    assert "isNearBottom" not in js, "the pinned-to-bottom gate must be gone"
    assert "window.scrollY" not in js, (
        "nothing in app.js measures the page scroll offset anymore"
    )


def test_scroll_helper_is_unconditional() -> None:
    """scrollReveal is still the ONE scrollIntoView in app.js, but it now
    scrolls unconditionally — no force-or-near-bottom condition in its
    body, and the phase-18 `force` parameter is gone. A page scroll can
    only ever happen where scrollReveal is CALLED (submit + restore)."""
    js = _js()
    body = _fn_body(js, "scrollReveal")
    assert "scrollIntoView" in body
    assert 'block: "end"' in body
    assert "if (" not in body, "the helper must have no gate — it scrolls when called"
    assert "force" not in body, "the phase-18 force parameter must be gone"
    # Still smooth / reduced-motion-aware through the default behavior.
    assert "behavior = SCROLL" in body
    # The regression pin: exactly one actual scrollIntoView CALL in the
    # whole file, and it lives inside scrollReveal (the word may appear
    # in comments; the call must not).
    assert js.count(".scrollIntoView(") == 1, (
        "app.js must call scrollIntoView exactly once (inside scrollReveal)"
    )
    assert js.find(".scrollIntoView(") > js.find("function scrollReveal")


def test_add_message_takes_explicit_scroll_intent() -> None:
    """addMessage(who, html, scroll = false): the phase-18
    scrollBehavior/force parameters are gone; the bubble scrolls only
    when the caller explicitly asks (submit reveal, restore landing)."""
    js = _js()
    body = _fn_body(js, "addMessage")
    assert "function addMessage(who, html, scroll = false)" in body
    assert "if (scroll) scrollReveal(wrap)" in body
    assert "force" not in body
    assert "scrollBehavior" not in body


def test_submit_reveals_user_message() -> None:
    """User intent kept by the owner: submitting scrolls the viewport down
    so the user's own message is visible — the submit addMessage passes
    the scroll intent; the streaming brain-bubble creations in the same
    function never do."""
    js = _js()
    send = js.find("async function handleSend")
    assert send != -1, "handleSend must exist"
    body = js[send : js.find("\n}\n", send)]
    assert 'addMessage("user", renderMarkdown(text), true)' in body, (
        "the submit must reveal the user message (scroll intent true)"
    )
    for call in re.findall(r'addMessage\("brain"([^)]*)\)', body):
        assert "true" not in call, (
            f"streaming brain bubbles must not scroll the page: {call!r}"
        )


def test_streaming_handlers_never_scroll_the_page() -> None:
    """The heart of the phase-42 contract: the thinking / tool / delta
    branches contain NO page-scroll call (no scrollReveal, no raw
    scrollIntoView). The thinking branch keeps the block-INTERNAL pin
    (textEl.scrollTop — phase 17, reworked in phase 43): that scrolls
    the block's own clip, not the page."""
    js = _js()
    think = js.find('ev.type === "thinking"')
    tool = js.find('ev.type === "tool"')
    delta = js.find('ev.type === "delta"')
    done = js.find('ev.type === "done"')
    assert -1 < think < tool < delta < done, "the turn handler must branch in order"
    for name, branch in (
        ("thinking", js[think:tool]),
        ("tool", js[tool:delta]),
        ("delta", js[delta:done]),
    ):
        assert "scrollReveal" not in branch, f"the {name} branch must not scroll the page"
        assert ".scrollIntoView(" not in branch, (
            f"the {name} branch must not scroll the page"
        )
    # The thinking window pin survives (phase 17 — untouched by this phase).
    thinking_branch = js[think:delta]
    assert "textEl.scrollTop = textEl.scrollHeight" in thinking_branch
    assert js.count("textEl.scrollTop = textEl.scrollHeight") == 1


def test_restore_landing_is_one_shot() -> None:
    """The phase-14 restore landing keeps its one-shot scroll
    (owner-kept): both restore call sites pass the explicit scroll
    intent and they are the only two restore scrolls; with the submit's
    single reveal, exactly three `true` intents exist in the whole file.
    The old forced "auto" landing is gone, and the one-shot, load-time
    contract is documented at the call site."""
    js = _js()
    body = _fn_body(js, "renderStoredMessage")
    assert 'addMessage("user", renderMarkdown(m.text), true)' in body
    assert 'addMessage("brain", renderMarkdown(m.text), true)' in body
    assert js.count('"auto", true') == 0, "the old forced 'auto' landing must be gone"
    # Submit reveal + the two restore landings — nothing else scrolls.
    assert js.count(", true)") == 3, "only submit + the two restore calls may scroll"
    # The marker comment documents the one-shot, load-time contract.
    assert "restore landing" in body
    assert "one-shot" in body


def test_typing_bubble_does_not_scroll() -> None:
    """A typing indicator appearing must not yank the page — the phase-18
    scrollReveal call in addTyping is removed with the gate."""
    js = _js()
    body = _fn_body(js, "addTyping")
    assert "scrollReveal" not in body
    assert ".scrollIntoView(" not in body


def test_scroll_constant_reduced_motion_intact() -> None:
    """The SCROLL constant is untouched (calm, don't remove): smooth by
    default, "auto" under prefers-reduced-motion — the two kept scroll
    call sites ride it as the default behavior."""
    js = _js()
    assert 'const SCROLL = reducedMotion ? "auto" : "smooth";' in js
    assert 'matchMedia("(prefers-reduced-motion: reduce)")' in js
    assert "Calm, don't remove" in js


def test_turn_end_focus_does_not_scroll() -> None:
    """The turn-end focus-back (phase 06's "always focus back") must not
    move the viewport: focusing the composer while the user is scrolled
    up would yank them to the bottom at the moment the turn ends.
    preventScroll keeps the keyboard flow without the scroll."""
    js = _js()
    finally_idx = js.find("// done | error → idle: always settle, always focus back")
    assert finally_idx != -1, "the turn's finally block must exist"
    block = js[finally_idx : js.find("\n}", finally_idx)]
    assert 'input.focus({ preventScroll: true })' in block
    assert "input.focus()" not in block