From 32855a95e11032302f8d24036f6f2dd44b829368 Mon Sep 17 00:00:00 2001 From: Christophe Besson Date: Tue, 1 Sep 2026 23:34:49 +0200 Subject: fix(hub): let the reader scroll up in the chat again The chat could not be read back: any wheel gesture was undone in the frame it happened in, and the "jump to latest" button never appeared. None of the pins in ChatPanel are at fault -- every one of them is guarded by "only if the reader is at the bottom". The reader never got to stop being at the bottom. fit() set the panel's height, read documentElement.scrollHeight back and subtracted the overflow, so the document alternately did and did not overflow the window. The page scrollbar appeared and vanished with it and visualViewport fired resize at every pass -- the event fit() is bound to. It therefore re-entered itself for the life of the panel: measured at 240 firings in two seconds on a page nobody was touching, against 2 for a bare document. Each pass ran fitAndPin, which re-pinned the list to the bottom before the scroll event that would have recorded the gesture was delivered a frame later, so atBottomRef never went false. - fit() learns the space below the panel once and remembers it on the element instead of re-deriving it by writing and measuring back. At the steady state it writes nothing, so it produces no resize. A real window resize or an orientation change forgets the learnt value and measures again (the page under the panel may have reflowed); visualViewport deliberately does not, since a phone fires it constantly. - The scroll-to-bottom is now scoped to *arrival*, which is all it was ever for: opening the group, or coming back to the Chat tab, including the thumbnails and link-preview cards that keep growing the list for a second afterwards. It ends when the reader takes hold of the scroll, and the ResizeObserver disconnects there. - That release is recorded from the gesture (wheel/touchmove/pointerdown/ keydown), not from the scroll event, which arrives too late to protect anything. Unchanged: landing on the newest message, following new messages while already at the bottom, the "load older" anchor and the unread marker. tests/harness/chat_scroll_probe.py mounts the real ChatPanel in a browser and reads a conversation back; test_chat_scroll_up.py asserts against it. With the fix reverted, five of its six tests fail and the sixth -- landing on the newest message -- still passes, which is the property that must not have been traded away. A structural test cannot see any of this, which is why it is measured. test_layout_responsive.py pinned the listener's name and follows the rename. Co-Authored-By: Claude Opus 5 Claude-Session: https://claude.ai/code/session_01W8oRqEHhnKUr1NfmTVdcyL --- .../meshbay-hub/tests/harness/chat_scroll_probe.py | 222 +++++++++++++++++++++ packages/meshbay-hub/tests/test_chat_scroll_up.py | 102 ++++++++++ .../meshbay-hub/tests/test_layout_responsive.py | 15 +- 3 files changed, 335 insertions(+), 4 deletions(-) create mode 100644 packages/meshbay-hub/tests/harness/chat_scroll_probe.py create mode 100644 packages/meshbay-hub/tests/test_chat_scroll_up.py (limited to 'packages/meshbay-hub/tests') diff --git a/packages/meshbay-hub/tests/harness/chat_scroll_probe.py b/packages/meshbay-hub/tests/harness/chat_scroll_probe.py new file mode 100644 index 0000000..7373976 --- /dev/null +++ b/packages/meshbay-hub/tests/harness/chat_scroll_probe.py @@ -0,0 +1,222 @@ +#!/usr/bin/env python3 +""" +Can the reader scroll up in the chat, and does the panel sit still when nobody +is touching it? + +`scroll_probe.py` answers "is the document taller than the window". This one +mounts **the real `ChatPanel`** — the shipped module, not a model of it — in a +browser, drives it the way a person does, and reports where the list ends up. + +It exists because the defect it was written for is invisible to every other kind +of test here. `fit()` set the panel's height, read the document's overflow back +and subtracted it, so the document alternately did and did not overflow the +window; the page scrollbar appeared and vanished with it, `visualViewport` fired +`resize` at each pass, and `fit()` is bound to that event. It therefore re-ran +about 120 times a second for the life of the panel, re-pinning the list to the +bottom every time — which undid each attempt to scroll up *inside the same +frame*, before the `scroll` event that would have recorded it was delivered. The +source reads as correct: every pin is guarded by "only if the reader is at the +bottom", and the reader never got to stop being at the bottom. + + chat_scroll_probe.py + +Prints JSON: an `idle` block (viewport-resize firings on a page nobody touches) +and a `steps` list (scroll position after each stage of a reading session). +""" +import http.server +import json +import socketserver +import subprocess +import sys +import tempfile +import threading +import time +from pathlib import Path + +STATIC = Path(__file__).resolve().parents[2] / "src" / "meshbay_hub" / "static" +PORT = 8747 +RECORDS = [] +socketserver.TCPServer.allow_reuse_address = True + +# A bare document fires a couple of these while it settles. Anything above this +# is the panel driving itself. +IDLE_RESIZE_CEILING = 20 + +PAGE = r""" + + +
+

a group

a description

+
+
+
+""" + + +class H(http.server.BaseHTTPRequestHandler): + def log_message(self, *a): + pass + + def do_POST(self): + RECORDS.append(json.loads( + self.rfile.read(int(self.headers["Content-Length"])).decode())) + self.send_response(204) + self.end_headers() + + def do_GET(self): + if self.path == "/": + body, ctype = PAGE.encode(), "text/html; charset=utf-8" + else: + path = (STATIC / self.path.lstrip("/")).resolve() + if not str(path).startswith(str(STATIC)) or not path.is_file(): + self.send_response(404) + self.end_headers() + return + body = path.read_bytes() + ctype = ("text/css" if path.suffix == ".css" + else "text/javascript" if path.suffix == ".js" + else "application/octet-stream") + self.send_response(200) + self.send_header("Content-Type", ctype) + self.send_header("Content-Length", str(len(body))) + self.end_headers() + self.wfile.write(body) + + +def main() -> int: + with socketserver.TCPServer(("127.0.0.1", PORT), H) as srv: + threading.Thread(target=srv.serve_forever, daemon=True).start() + with tempfile.TemporaryDirectory() as profile: + # Real time, not `--virtual-time-budget`: the defect is a feedback + # loop between layout and an event, and a virtual clock does not + # run it. + proc = subprocess.Popen( + ["google-chrome", "--headless=new", "--disable-gpu", "--no-sandbox", + f"--user-data-dir={profile}", "--window-size=1100,800", + f"http://127.0.0.1:{PORT}/"], + stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL) + for _ in range(300): + if RECORDS: + break + time.sleep(0.1) + proc.terminate() + try: + proc.wait(timeout=10) + except subprocess.TimeoutExpired: + proc.kill() + if not RECORDS: + print(json.dumps({"error": "no measurement"}), file=sys.stderr) + return 1 + print(json.dumps(RECORDS[0], indent=1)) + return 0 + + +if __name__ == "__main__": + raise SystemExit(main()) diff --git a/packages/meshbay-hub/tests/test_chat_scroll_up.py b/packages/meshbay-hub/tests/test_chat_scroll_up.py new file mode 100644 index 0000000..6cafcdc --- /dev/null +++ b/packages/meshbay-hub/tests/test_chat_scroll_up.py @@ -0,0 +1,102 @@ +""" +Reading back through the conversation must work. + +The scroll-to-bottom on arrival has been patched five times, and the sixth +patch took the other side away: the panel re-pinned the list about 120 times a +second, so a wheel gesture was undone in the frame it happened in and the older +messages became unreachable. Every pin in the source is guarded by "only if the +reader is at the bottom" — the reader simply never got to stop being at the +bottom, because the `scroll` event that records it is delivered a frame after +the pin that erased it. + +None of that is visible in the source, which is why this measures the real +`ChatPanel` in a browser instead of reading `chat-app.js`. `test_chat_scroll_ +bottom.py` keeps the structural guards; this one keeps the behaviour. +""" +import json +import shutil +import subprocess +from pathlib import Path + +import pytest + +HARNESS = Path(__file__).parent / "harness" / "chat_scroll_probe.py" +STATIC = Path(__file__).resolve().parents[1] / "src" / "meshbay_hub" / "static" + +pytestmark = pytest.mark.skipif( + shutil.which("google-chrome") is None or not (STATIC / "chat-app.js").exists(), + reason="Chrome or the SPA sources are not available") + +# A bare document fires a couple of these as it settles. Anything above this is +# the panel driving itself, which is what the loop looked like. +IDLE_RESIZE_CEILING = 20 + +# The harness scrolls up by six frames of 120px. Chrome's scroll anchoring +# moves the reader with the content when preview cards land above them, so the +# distance from the bottom is not expected to be exactly 720 afterwards — only +# to stay well clear of it. +SCROLLED_UP_FLOOR = 400 + + +@pytest.fixture(scope="module") +def probe(): + run = subprocess.run(["python3", str(HARNESS)], capture_output=True, timeout=180) + assert run.returncode == 0, run.stderr.decode()[-2000:] + data = json.loads(run.stdout.decode()) + return data, {s["label"]: s for s in data["steps"]} + + +def test_arrives_on_the_newest_message(probe): + """Opening the tab lands at the end of the conversation, after the late + layout and the panel sizing itself.""" + _, steps = probe + assert steps["arrived"]["fromBottom"] < 40, ( + "the chat must open on the newest message; it opened " + f"{steps['arrived']['fromBottom']}px above it") + + +def test_the_panel_does_not_resize_itself(probe): + """fit() runs on `resize` and must not produce one. When it did, it re-ran + every frame and re-pinned the scroll with it.""" + data, _ = probe + assert data["idle"]["viewportResizes"] <= IDLE_RESIZE_CEILING, ( + f"{data['idle']['viewportResizes']} viewport resizes on a page nobody " + "touched -- fit() is feeding the event it listens for, and every pass " + "re-pins the chat to the bottom") + assert data["idle"]["documentOverflow"] <= 0, ( + "the chat tab must not leave the document taller than the window") + + +def test_scrolling_up_holds(probe): + """The gesture must survive the frame it happened in.""" + _, steps = probe + assert steps["scrolled up"]["fromBottom"] >= SCROLLED_UP_FLOOR, ( + "scrolling up was undone: the list came back to " + f"{steps['scrolled up']['fromBottom']}px from the bottom") + assert steps["scrolled up"]["jumpButton"], ( + "the panel never noticed the reader leave the bottom -- the pin beat " + "the scroll event, so atBottom stayed true and no jump button appeared") + + +def test_late_content_does_not_drag_the_reader_down(probe): + """Link previews and thumbnails arrive over the following seconds and grow + the list. That is what the arrival pin is for, and it must be over by + now.""" + _, steps = probe + assert steps["previews landed"]["fromBottom"] >= SCROLLED_UP_FLOOR, ( + "preview cards landing pulled the reader back to the bottom") + + +def test_a_new_message_does_not_yank_the_reader_down(probe): + """Somebody writing while you read back marks the spot; it does not move + you.""" + _, steps = probe + assert steps["message arrived"]["fromBottom"] >= SCROLLED_UP_FLOOR, ( + "an incoming message pulled the reader away from what they were reading") + + +def test_a_resize_does_not_yank_the_reader_down(probe): + """A window resize, a rotation, or a phone's URL bar collapsing.""" + _, steps = probe + assert steps["window resized"]["fromBottom"] >= SCROLLED_UP_FLOOR, ( + "a resize pulled the reader back to the bottom") diff --git a/packages/meshbay-hub/tests/test_layout_responsive.py b/packages/meshbay-hub/tests/test_layout_responsive.py index d7a680d..4ee07d0 100644 --- a/packages/meshbay-hub/tests/test_layout_responsive.py +++ b/packages/meshbay-hub/tests/test_layout_responsive.py @@ -145,12 +145,19 @@ def test_the_measurement_survives_a_scrolled_page(app): def test_the_panel_refits_when_the_viewport_changes(app): - # `fit` is wrapped by `fitAndPin` (which also keeps the view pinned to - # the bottom on a resize) — that is what the listeners bind to. + # `fit` is wrapped by `fitAndPin` (which also keeps the view pinned to the + # bottom on a resize), and on the window by `refit`, which additionally + # forgets the learnt space below the panel — a real viewport change can + # mean the page under it reflowed. `visualViewport` deliberately does not + # forget: a phone fires that event constantly, and re-deriving the leftover + # there is what made fit() oscillate and weld the reader to the bottom of + # the conversation (see test_chat_scroll_up.py). for event in ("resize", "orientationchange"): - assert f"addEventListener('{event}', fitAndPin)" in app + assert f"addEventListener('{event}', refit)" in app assert "visualViewport?.addEventListener('resize', fitAndPin)" in app - assert "removeEventListener('resize', fitAndPin)" in app, "the listener must be released" + assert "removeEventListener('resize', refit)" in app, "the listener must be released" + assert "el._chatFitBelow = 0" in app, ( + "a window resize must forget the learnt leftover and measure it again") def test_the_css_floor_does_not_fight_the_measurement(css, app): -- cgit v1.2.3