[NoQA] feat: Add ManualSendMessageVisible subspans

[LukasMod]

Explanation of Change

This partitions ManualSendMessageVisible into three sequential child spans. They do not overlap and their
durations sum to the parent, so each accounts for one stage.

ManualSendMessageVisible_<reportActionID>   t0 → t3
├─ ManualSendMessageSubmit                  t0 → t1
├─ ManualSendMessagePropagate               t1 → t2
└─ ManualSendMessagePaint                   t2 → t3

Mark	Where
t0	top of addComment, src/libs/actions/Report/index.ts:1250
t1	immediately after API.write(...) returns, src/libs/actions/Report/index.ts:1160
t2	TextCommentFragment's layout effect, which React runs synchronously during the commit
t3	TextCommentFragment's onLayout handler

Both render-side boundaries are keyed on the sent message's own reportActionID and marked by a component
that already receives it. Nothing infers which row the sent message is, and no list item renderer carries
telemetry.

What each phase measures

Phase	From / to	Contains	Does not contain
Submit	addComment entry to API.write returning	Markdown to HTML, the optimistic report action, snapshot and ancestor optimistic data, the last-visible scans, request assembly, queue push	The Onyx write. API.write only enqueues and Onyx.merge defers the merge, so nothing is persisted and nothing has rendered yet
Propagate	the write being enqueued to React committing the sent row	Onyx's deferred merge, the derived recomputes it triggers, subscriber notification, React scheduling, and React's render and commit	The visibleReportActions recompute, which lands in Paint
Paint	React's commit to the platform reporting layout	Browser style recalculation, layout and paint, any main-thread work delaying them, ResizeObserver delivery	Application render work for the sent row

Propagate ending is not the message becoming visible. t2 is a useLayoutEffect, which React runs
synchronously inside the commit, before the browser has done any layout or paint work. t3 is the earliest
point at which the row can be confirmed laid out.

What this does and does not answer

Being explicit, because the value here is narrower than "the spans will show why sends are slow".

Propagate is the only phase that contains yield points, so contention lands there structurally rather than
as a finding. Across eleven measured sends it was dominant every time, at 68 to 87% of the parent. Inside it,
roughly 60% of a send sits in gaps that carry no spans at all, and separating the causes there needs a
main-thread profile, not more spans.

What the split does deliver:

• Failure separated from slowness. Submit present, Propagate absent, parent canceled means the
  optimistic action never reached a list. That is a countable Sentry query rather than an anecdote, and today
  the two cases share one number.
• Three causes ruled out and kept ruled out. Submit measured under 1% of the parent in every send and
  was flat between a light account and a heavy account on a two-deep RHP stack, so the optimistic builders
  are not a scaling problem. React's render and commit of the sent row measured 2 to 5%. The derived cascade
  measured 11.5 to 47ms and did not grow with scenario weight.
• A verification harness. Any change in this area either shrinks Propagate and the parent together, or
  moves nothing. Submit and Paint staying flat is what confirms a win is real rather than a shift between
  stages.

Coverage limits: only sends made while scrolled to the bottom are measured, since the parent span does not
start otherwise. No phase covers time after the message is visible. The keypress to addComment interval
sits outside the parent.

Implementation notes

• New module src/libs/telemetry/sendMessageSpans.ts, following the existing single-purpose span-helper
  pattern (markSubmitExpenseEnd.ts, startScanProcessSpan.ts). No module state. activeSpans is the
  registry: getSpan(phaseId) answers whether a phase is running, which also makes every function
  self-healing, since once the parent is cancelled every later call for that send is a no-op.
• Phase ids are prefixed with ManualSendMessage, so the existing cancelSpansByPrefix sweeps already
  match them.
• Phases parent to ManualSendMessageVisible only. The effect-anchored ManualSendMessage keeps no
  children, so the A/B comparison in feat: Add ManualSendMessageVisible #97789 stays clean and nothing here moves when that span is retired.
• t2 must stay a layout effect. A passive effect is scheduled with no paint guarantee and drifts by an
  unknown amount, charging part of Paint to Propagate.
• Sentry drops child spans still running when their parent ends, so the paths that end the parent close the
  phases first: onLayout on the happy path, the skeleton listener on the cancel path, and
  cancelSpansByPrefix, which now cancels in reverse insertion order. Reverse is children-first because a
  child is always registered after the parent it hangs off. cancelAllSpans is left in insertion order on
  purpose: it sweeps every span family, so reversing it would start surfacing other features' cancelled
  children with abort-time durations. A send interrupted by an AppState transition therefore still loses its
  open phase, which the reading guide in the investigation doc calls out.
• A fourth phase isolating React's render and commit of the sent row was built, measured and then dropped
  before this PR. It required a mutation in the render body of ReportActionsListItemRenderer, which a
  discarded concurrent render would anchor one pass early, and it measured 2 to 5% and was never dominant.
  Its finding is recorded in the investigation doc instead of being re-measured on every send.

Cost is three additional spans per send. Runtime overhead is two activeSpans map lookups and one span
object per phase, none of it on a render hot path.

Fixed Issues

$
PROPOSAL:

Tests

• Verify that no errors appear in the JS console

Offline tests

QA Steps

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
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• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
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    • If any non-english text was added/modified, I used JaimeGPT to get English > Spanish translation. I then posted it in #expensify-open-source and it was approved by an internal Expensify engineer. Link to Slack message:
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Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

[codecov]

Codecov Report

❌ Looks like you've decreased code coverage for some files. Please write tests to increase, or at least maintain, the existing level of code coverage. See our documentation here for how to interpret this table.

Files with missing lines	Coverage Δ
src/CONST/index.ts	94.81% <ø> (ø)
src/hooks/useCancelSendMessageSpanOnSkeleton.ts	100.00% <100.00%> (ø)
src/libs/actions/Report/index.ts	72.24% <100.00%> (+0.52%)	⬆️
src/libs/telemetry/activeSpans.ts	94.64% <92.30%> (+0.41%)	⬆️
...ox/report/ReportActionCompose/useComposerSubmit.ts	67.16% <0.00%> (ø)
...pages/inbox/report/comment/TextCommentFragment.tsx	77.96% <66.66%> (-2.43%)	⬇️
src/libs/telemetry/sendMessageSpans.ts	65.71% <65.71%> (ø)
... and 19 files with indirect coverage changes

[LukasMod]

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