desktop+ui: the window opens on B2's ground, and a launch is measurable (GH #225) - #228
desktop+ui: the window opens on B2's ground, and a launch is measurable (GH #225)#228samkeen wants to merge 2 commits into
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…le (GH #225) The window is shown as soon as it exists, which is long before the webview has a stylesheet, so a launch begins with the platform's white. This does not hide the window — that was tried and reverted, and it fails for a reason that has not gone away: WebKit throttles `requestAnimationFrame` in an offscreen page, so "reveal when real pixels exist" never fires and the safety timer becomes the launch time. It gives the window a ground instead. Two surfaces, one colour, because they are painted by different things at different moments. `launch::ground` dresses the *window* from the OS theme before the event loop runs; that is the only half no frontend change can reach, and it is painted over the instant the webview draws an unstyled document white on top of it. So `index.html` carries the same two values in a cascade layer for the *document*, which is what survives from then on — CSS with no script, since the CSP grants no inline script and script-src is not something a Markdown renderer loosens (ADR-0016). The honest limit: both layers ask the OS, and a theme pinned in Settings lives in localStorage, which the host cannot see and must not (a viewing choice is never host state). Right for the System default and for a pin that agrees with the OS; a pin that disagrees still gets one ground change when `loadTheme` runs, which is what it gets today on top of the white. That colour pair now exists in three places, so two tests make the duplication checked rather than merely regretted: `ground.test.ts` reads index.html against style.css, and `ground_matches_the_stylesheet` reads style.css against the Rust consts. Both were confirmed to fail on a one-hex drift. The issue asks for before-and-after numbers, and a launch spans two clocks with only one sink. `b2::launch` is that measurement: five marks on one Unix-epoch axis under the existing B2_LOG_FILE dataset — `window-ready`, `page-load-started`, `page-load-finished` from the host, then `boot-start` and `first-frame` from the webview via `launch_mark`, sent after the frame they time so the probe never adds the latency it is measuring. Deliberately not done: revealing the window on a signal. `Builder::on_page_load` does fire host-side and so is immune to the throttle that killed the last attempt, but `Finished` is the document, not the app — it would reveal a window showing the ground and nothing else. That is a decision to take on the numbers this change makes it possible to have, not ahead of them. Co-Authored-By: Claude <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Jq9rgD3ckbaPd3pdXQk53z
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📝 WalkthroughWalkthroughThe desktop adapter adds launch background grounding and timing instrumentation. Host and webview milestones use Unix-epoch milliseconds and the ChangesDesktop launch observability
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🔵 Low · up to Launch measurements for webview milestones currently include IPC delay in the event-time field, which can misstate before-and-after startup numbers. The change is otherwise mergeable with explicit owner awareness and follow-up on the telemetry fields. Sequence Diagram(s)sequenceDiagram
participant Webview
participant Tauri
participant b2_launch as b2::launch
Webview->>Webview: Capture boot-start timestamp
Webview->>Tauri: Send boot-start and first-frame marks
Tauri->>b2_launch: Forward webview timestamps
b2_launch-->>b2_launch: Emit tracing records
Suggested reviewers: Poem
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Full details: Docstring CoverageExplanation Docstring coverage is 88.24% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 17 functions across 6 files. (3 skipped: 3 unsupported.) ✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
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Inline comments:
In `@crates/b2-desktop/src/launch.rs`:
- Around line 85-86: Update webview_mark so epoch_ms stores the webview-recorded
event timestamp, while the host receipt timestamp is stored in a separate field;
preserve the documented query’s use of epoch_ms for all five marks.
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…arrived Addresses CodeRabbit on #228. `webview_mark` put the host's receipt time in `epoch_ms` and the webview's own reading in `webview_epoch_ms` — so the field meant "when it happened" on the three host marks and "when it arrived" on the two webview ones, and the query in the module doc reads `epoch_ms` for all five. `boot-start` and `first-frame` therefore each came out carrying an IPC hop they did not spend: the instrument reporting its own latency as the app's, which is precisely what the old doc comment claimed it avoided. `epoch_ms` is now the event time on every mark, whichever side timed it, and the receipt is kept beside it as `received_epoch_ms` — dropping it would lose the only evidence that the hop was ordinary, and a launch where it isn't is a launch to distrust. No test: pinning a tracing record's field names needs a global subscriber, and this crate's suite is one binary running in parallel — the race CLAUDE.md already documents for the two core tests that own their own binaries. The field names now say which is which, which is the cheaper guard. Co-Authored-By: Claude <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Jq9rgD3ckbaPd3pdXQk53z
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Closing this unmerged. It was tested on a real launch and it does not fix the bug for the people who have it. Pinned Dark still shows a white screen, then the dark UI. Light mode looks right. That is the limit this PR documented, and shipping it would have been the wrong call: a dark-mode user is precisely who notices a white flash, so the change makes launch tidier for the case that barely needed it and leaves the reported bug intact for the case that does. "Right for the System default" was true and beside the point. Why it fails is not a defect in the code — both layers do what they claim, and both ask the wrong question. Whatever comes next has to read the pin, which means one of:
The Failure reported on #225. Generated by Claude Code |
2 participants
The window is shown as soon as it exists, which is long before the webview
has a stylesheet, so a launch begins with the platform's white. This does not
hide the window — that was tried and reverted, and it fails for a reason that
has not gone away: WebKit throttles
requestAnimationFramein an offscreenpage, so "reveal when real pixels exist" never fires and the safety timer
becomes the launch time. It gives the window a ground instead.
Two surfaces, one colour, because they are painted by different things at
different moments.
launch::grounddresses the window from the OS themebefore the event loop runs; that is the only half no frontend change can
reach, and it is painted over the instant the webview draws an unstyled
document white on top of it. So
index.htmlcarries the same two values in acascade layer for the document, which is what survives from then on — CSS
with no script, since the CSP grants no inline script and script-src is not
something a Markdown renderer loosens (ADR-0016).
The honest limit: both layers ask the OS, and a theme pinned in Settings lives
in localStorage, which the host cannot see and must not (a viewing choice is
never host state). Right for the System default and for a pin that agrees with
the OS; a pin that disagrees still gets one ground change when
loadThemeruns, which is what it gets today on top of the white.
That colour pair now exists in three places, so two tests make the duplication
checked rather than merely regretted:
ground.test.tsreads index.htmlagainst style.css, and
ground_matches_the_stylesheetreads style.css againstthe Rust consts. Both were confirmed to fail on a one-hex drift.
The issue asks for before-and-after numbers, and a launch spans two clocks
with only one sink.
b2::launchis that measurement: five marks on oneUnix-epoch axis under the existing B2_LOG_FILE dataset —
window-ready,page-load-started,page-load-finishedfrom the host, thenboot-startandfirst-framefrom the webview vialaunch_mark, sent after the frame theytime so the probe never adds the latency it is measuring.
Deliberately not done: revealing the window on a signal.
Builder::on_page_loaddoes fire host-side and so is immune to the throttle that killed the last
attempt, but
Finishedis the document, not the app — it would reveal awindow showing the ground and nothing else. That is a decision to take on the
numbers this change makes it possible to have, not ahead of them.
Co-Authored-By: Claude noreply@anthropic.com
Claude-Session: https://claude.ai/code/session_01Jq9rgD3ckbaPd3pdXQk53z
Summary by CodeRabbit
New Features
Documentation
Tests