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). Both user-intent scrolls land at
the DOCUMENT BOTTOM (scrollReveal's `window.scrollTo`): the old
`scrollIntoView({ block: "end" })` aligned the message's bottom to the
viewport bottom — which sits above the in-flow composer — so every
submit hopped the page UP by the composer+footer height and pushed the
composer below the fold.

The JS behavior itself is E2E-covered
(tests/e2e/test_no_reply_autoscroll.py); here we pin the source markers
of the contract — the phase-18 gate is gone (no NEAR_BOTTOM_PX /
isNearBottom), scrollReveal scrolls unconditionally and is the single
page scroll in app.js (a document-bottom `window.scrollTo` — no
`scrollIntoView` call remains), 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 (or to the
upward-hopping block:"end" reveal) 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 page-level band constant, no gate
    function, and no document-scroller measurement left anywhere in
    app.js. (The phase-43 window-level THINKING_NEAR_BOTTOM_PX /
    isThinkingNearBottom pair is a different band — the thinking
    window's, not the page's.)"""
    js = _js()
    assert not re.search(r"(?<![A-Z_])NEAR_BOTTOM_PX\b", js), (
        "the 200px page-level 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 page scroll in app.js, and it
    scrolls unconditionally — no gate in its body, and the phase-18
    `force` parameter is gone. A page scroll can only ever happen where
    scrollReveal is CALLED (submit + restore). It lands at the document
    BOTTOM via `window.scrollTo`: the old `scrollIntoView({ block:
    "end" })` aligned the message's bottom to the viewport bottom, which
    sits above the in-flow composer, so every submit hopped the page UP
    by the composer+footer height (the "Enter scrolls the page up"
    bug) — no `scrollIntoView` call may remain."""
    js = _js()
    body = _fn_body(js, "scrollReveal")
    assert "window.scrollTo(" in body
    assert "document.documentElement.scrollHeight" 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"
    assert 'block: "end"' not in body, (
        "the upward-hopping block:'end' alignment must be gone"
    )
    # Still smooth / reduced-motion-aware through the default behavior.
    assert "behavior = SCROLL" in body
    # The regression pins: no scrollIntoView call anywhere in the file,
    # and the one window.scrollTo call lives inside scrollReveal.
    assert js.count(".scrollIntoView(") == 0, (
        "app.js must not call scrollIntoView — the document-bottom "
        "scrollTo replaces the block:'end' reveal"
    )
    assert js.count("window.scrollTo(") == 1
    assert js.find("window.scrollTo(") > js.find("function scrollReveal")


def test_add_message_takes_explicit_scroll_intent() -> None:
    """addMessage(who, html, scroll = false, image = null): the phase-18
    scrollBehavior/force parameters are gone; the bubble scrolls only
    when the caller explicitly asks (submit reveal, restore landing).
    Phase 123 (task 02) appended the optional `image` argument (the
    question's attached image — { src, alt } on a user bubble, the ONE
    renderer for live + restore + shared); the scroll contract is
    untouched."""
    js = _js()
    body = _fn_body(js, "addMessage")
    assert "function addMessage(who, html, scroll = false, image = null)" 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
    turn handler never do.

    Phase 49: the turn handler is runTurn (extracted from handleSend) —
    the user append + persistence save point 1 sit in its `!reask`
    block (the redo-in-place retry path skips both: the question is
    already in the DOM + conversation)."""
    js = _js()
    turn = js.find("async function runTurn")
    assert turn != -1, "runTurn must exist (phase 49 extraction)"
    body = js[turn : js.find("\n}\n", turn)]
    assert "if (!reask) {" in body, "the user append is gated on !reask"
    # Phase 123 (task 02): the user append gained the optional image
    # argument (the attached image's { src, alt }) — the call is
    # multi-line now; the contract is the same: user + the raw text +
    # the explicit scroll intent true.
    assert re.search(
        r'addMessage\(\s*"user",\s*renderMarkdown\(text\),\s*true', 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
    # Phase 182 (task 07): the brain renderer gained the verbatim option —
    # the SCROLL intent (the trailing `true`) is untouched, and the option
    # object (`{ verbatim: true }`) never ends in `", true)"`, so the count
    # below still counts the two restore landings alone.
    assert 'addMessage("brain", renderMarkdown(m.text, { verbatim: true }), 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.
    # Phase 123 (task 02): the submit call is multi-line (the optional
    # image argument follows the scroll intent), so it no longer ends
    # in the single-line ", true)" literal — the two restore calls do;
    # the submit reveal is counted by its own (multi-line) shape.
    assert js.count(", true)") == 2, (
        "only the two restore calls may scroll (single-line shape)"
    )
    assert len(re.findall(r'addMessage\(\s*"user",\s*renderMarkdown\(text\),\s*true', js)) == 1, (
        "the submit reveal may scroll (multi-line since phase 123's image argument)"
    )
    # 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.

    Phase 143 (TODO L5): the focus-back is now GATED on pointer type —
    `if (!COARSE_POINTER) input.focus({ preventScroll: true })`. On a
    coarse pointer (phone/tablet) focusing the composer pops the
    virtual keyboard over the completed answer, so the composer stays
    unfocused there (the ≥44px tap target starts the next question).
    This pin's job: the focus-back exists, is preventScroll (the
    phase-06/42 contract, byte-preserved on desktop), and is
    coarse-gated — a bare ungated `input.focus(...)` line in the
    finally block is a failure, as a missing or mistyped
    `COARSE_POINTER` constant is."""
    js = _js()
    # Phase 48: the settle line gained the user-stop terminal (stop →
    # idle, no banner) — the focus-back contract is unchanged.
    finally_idx = js.find("// done | error | stop → 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)]
    # Phase 143: the gated shape — the focus call exists, keeps
    # preventScroll, and is wrapped in the coarse-pointer gate.
    assert "if (!COARSE_POINTER) input.focus({ preventScroll: true })" in block
    # A bare, ungated focus line (the pre-phase-143 shape) is gone:
    # every focus call in the block rides the gate.
    focus_lines = [ln for ln in block.splitlines() if "input.focus(" in ln]
    assert focus_lines, "the turn-end focus-back must still exist"
    assert all("if (!COARSE_POINTER)" in ln for ln in focus_lines), (
        "the turn-end focus-back must be coarse-pointer gated (phase 143)"
    )
    assert "input.focus()" not in block
    # The L391-twin constant: the same typeof-guarded matchMedia shape
    # as reducedMotion, bound to COARSE_POINTER.
    assert re.search(
        r'const COARSE_POINTER\s*=\s*typeof matchMedia === "function"'
        r' && matchMedia\("\(pointer: coarse\)"\)\.matches;',
        js,
    )