test(app): add long-session input lag perf guard

[Astro-Han]

Summary

• Add a default-profile long-session-input-lag perf scenario.
• Seed a long session, focus the composer, type a fixed draft, and capture the existing PR0 perf metrics window.
• Lock the new scenario into the default profile with a unit test.

Why

#615 calls out typing lag in long sessions as a user-visible performance symptom, and #599 now tracks the May UI rewrite launch contract. Existing PR0 coverage protects streaming, tool expansion, scroll reading, timeline recompute, terminal open, and heavy default-open bash output, but did not directly measure composer typing inside a long session.

This PR adds that guard without changing UI behavior, message rendering, scroll ownership, virtualization, or diff rendering.

Related Issue

Related to #615 and #599.

Human Review Status

Pending. A human should make the final merge decision after reviewing the final diff and verification evidence.

Review Focus

Please focus on whether the scenario boundary is narrow enough: stable long-session fixture, reset after composer focus, fixed ASCII typing text, existing metrics capture, and default-profile routing only.

Risk Notes

Low. This only changes perf test coverage. It may add a small amount of runtime to the default perf probe workflow because the new scenario runs three browser samples.

How To Verify

Dependency install: bun install --frozen-lockfile completed successfully in the new worktree
TDD red: bun --cwd packages/app test ./e2e/perf/profiles.unit.ts failed before profile wiring because long-session-input-lag was not in the default profile
Profile unit: bun --cwd packages/app test ./e2e/perf/profiles.unit.ts -> 1069 pass, 0 fail
Focused perf e2e: bun --cwd packages/app test:e2e:local:perf -- --grep "long-session-input-lag" -> 1 passed
Typecheck: bun --cwd packages/app typecheck -> exit 0
Diff check: git diff --check -> exit 0

Screenshots or Recordings

Not required. This PR adds perf guard coverage only and does not change visible UI.

Checklist

• Human review status is stated above as pending, approved, or not required
• I linked the related issue, or stated why there is no issue
• This PR has type, primary area, and priority labels, or I requested maintainer labeling
• I described the review focus and any meaningful risks
• I listed the relevant verification steps and the key result for each
• I did not introduce unrelated refactors, dependencies, generated files, or file changes beyond the stated scope
• I manually checked visible UI or copy changes when needed, with screenshots or recordings
• I considered macOS and Windows impact for platform, packaging, updater, signing, paths, shell, or permissions changes
• I called out docs, release notes, dependencies, permissions, credentials, deletion behavior, generated content, or local file changes when relevant
• I reviewed the final diff for unrelated changes and suspicious dependency changes
• I am targeting dev, and my PR title and commit messages use Conventional Commits in English

Summary by CodeRabbit

• Tests
  • Added performance testing scenario to measure input responsiveness in extended chat sessions.

[github-actions]

Suggested priority: P3 (only low-risk paths changed (packages/app/e2e/perf/perf-probe.spec.ts, packages/app/e2e/perf/profiles.ts, packages/app/e2e/perf/profiles.unit.ts)).

P1/P0 are reserved for maintainer confirmation. Please relabel manually if this is a release blocker, security issue, data-loss risk, or updater/runtime failure.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 2bcc0191-524f-43c9-84d5-261d5979fb67

📥 Commits

Reviewing files that changed from the base of the PR and between 70eab76 and 9d495a1.

📒 Files selected for processing (2)

• packages/app/e2e/perf/perf-probe.spec.ts
• packages/app/e2e/perf/timeline-fixture.ts

📝 Walkthrough

Walkthrough

This PR adds a new performance scenario named long-session-input-lag that measures input latency in sessions with timeline recompute overhead. The scenario is defined as a union type, wired into the default profile configuration, implemented as a 3-run e2e test with a prompt text verification helper, and validated via unit tests.

Changes

Long-session input lag performance scenario

Layer / File(s)	Summary
Scenario type definition and profile wiring packages/app/e2e/perf/profiles.ts	PerfScenarioName union adds "long-session-input-lag" and defaultScenarios set includes it for non-low-end profile runs.
Long-session input lag test scenario packages/app/e2e/perf/perf-probe.spec.ts	Test constant inputLagText and helper readPromptText are added; the long-session-input-lag test case runs 3 times using a recompute-heavy session, types a prompt, asserts text match, and captures perf probe snapshots.
Profile coverage validation test packages/app/e2e/perf/profiles.unit.ts	Unit test confirms long-session-input-lag scenario runs under default profile but not low-end profile.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• Astro-Han/pawwork#609: Adds another perf-probe scenario test case (terminal-side-panel-open) to the same perf-probe test harness using shared helpers.
• Astro-Han/pawwork#608: Modifies perf-probe scenario run handling, cooldown, and result aggregation at the same test harness level.
• Astro-Han/pawwork#610: Extends the low-end perf-profile framework that this scenario wires into.

Poem

🐰 A scenario takes the stage, input lag measured through the page,
Prompt text flows with helper's grace, three runs trace the typing pace,
Default profile holds it tight, low-end skips it out of sight! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title clearly and specifically describes the main change: adding a new perf guard test for input lag in long sessions.
Description check	✅ Passed	The PR description follows the template structure with all key sections completed: summary, why, related issues, review focus, risk notes, verification steps, and checklist fully filled out.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/i615-input-lag-guard

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Review ran into problems

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[gemini-code-assist]

Code Review

This pull request introduces a new performance test scenario, "long-session-input-lag," designed to measure input responsiveness during long sessions with realistic message history. The changes include the test implementation in perf-probe.spec.ts, updates to the performance profile configurations, and a new unit test. Feedback was provided to replace the use of innerText with textContent in a helper function to avoid synchronous layout reflows that could introduce noise into the performance metrics.

[github-actions]

Perf delta summary

Comparator: pass

Profile / Scenario	interaction median	interaction worst	long task max	tbt	frame gap p95	frame gap max	jank count	cls	status
default / homepage-cold	48 -> 24 (-24)	48 -> 56 (+8)	73 -> 69 (-4)	23 -> 19 (-4)	33.3 -> 16.8 (-16.5)	133.3 -> 100.1 (-33.2)	3 -> 3 (0)	0 -> 0 (0)	pass
default / long-session-input-lag	48 -> 40 (-8)	48 -> 40 (-8)	0 -> 0 (0)	0 -> 0 (0)	16.8 -> 16.7 (-0.1)	16.8 -> 16.8 (0)	0 -> 0 (0)	0 -> 0 (0)	pass
default / session-streaming-long	40 -> 48 (+8)	80 -> 64 (-16)	0 -> 0 (0)	0 -> 0 (0)	16.8 -> 16.8 (0)	16.8 -> 16.8 (0)	0 -> 0 (0)	0 -> 0 (0)	pass
default / tool-call-expand	16 -> 24 (+8)	16 -> 24 (+8)	0 -> 0 (0)	0 -> 0 (0)	16.8 -> 16.7 (-0.1)	16.8 -> 16.7 (-0.1)	0 -> 0 (0)	0 -> 0 (0)	pass
default / tool-default-open-heavy-bash	32 -> 24 (-8)	32 -> 24 (-8)	66 -> 64 (-2)	16 -> 14 (-2)	50 -> 49.9 (-0.1)	100 -> 100 (0)	3 -> 3 (0)	0 -> 0 (0)	pass
default / terminal-side-panel-open	40 -> 48 (+8)	40 -> 56 (+16)	0 -> 0 (0)	0 -> 0 (0)	16.8 -> 16.8 (0)	16.8 -> 16.8 (0)	0 -> 0 (0)	0 -> 0 (0)	pass
default / session-scroll-reading	24 -> 24 (0)	24 -> 24 (0)	0 -> 0 (0)	0 -> 0 (0)	16.7 -> 16.8 (+0.1)	16.7 -> 16.8 (+0.1)	0 -> 0 (0)	0.505 -> 0.505 (0)	warn: cls
low-end / session-timeline-recompute	120 -> 120 (0)	136 -> 120 (-16)	110 -> 105 (-5)	165 -> 169 (+4)	83.3 -> 100.1 (+16.8)	166.7 -> 166.7 (0)	3 -> 3 (0)	0.081 -> 0.081 (0)	pass