perf(agent): read a shared scope's text once per snapshot

[Kikobeats]

Summary

• Controls that share a parent were each reading that parent's text twice (guard, then scopes). On a 400-cell grid that took the in-page snapshot from 47.6 ms to 11.4 ms, under the 29.9 ms baseline from v14.0.2.
• The memo lives only for the snapshot call. cache.guard() with no reader still reads live, so a text change after observe stays stale.
• shared scope text is read once per snapshot fails the agent test job if a shared scope is read once per action again. A wall-clock budget on the runner would flake; the read count is the cost that showed up.

Test plan

• pnpm exec ava test/snapshot.js (28 passed)
• Grid fixture, same Chrome, 1280×800: in-page p50 47.6 ms → 11.4 ms, 252 actions and 616 scopes unchanged
• CI: Test @browserless/agent

Made with Cursor

Summary by CodeRabbit

• Bug Fixes
  • Actions now use consistent text from their surrounding area when describing context, including when multiple actions share that area.
  • Changes to surrounding text are detected, helping prevent actions from proceeding with outdated context.
  • Scope text is limited in length to keep action context concise and readable, while preserving enough surrounding information to describe actions accurately.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 9b9fb613-e599-4ea5-ae63-c49b87d36c1a

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📥 Commits

Reviewing files that changed from the base of the PR and between 6dc080b and c8adf33.

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📒 Files selected for processing (2)

• .github/workflows/pull_request.yml
• packages/agent/test/chrome.js

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📝 Walkthrough

Walkthrough

Snapshot scope text is cached per snapshot call and shared by guard data and action scope summaries. Tests verify that shared scope text is read once and that text changes invalidate action freshness. A browser test compares snapshot timing with a base version.

Changes

Snapshot scope text

Layer / File(s)	Summary
Read and reuse scope text packages/agent/src/snapshot.js, packages/agent/test/snapshot.js	A snapshot-local reader caches scope text for guard data and action scope summaries. Guard text remains limited to 6,000 characters, and action scope summaries remain limited to 1,000 characters. Tests check that shared text is read once and that text changes invalidate action freshness.
Compare snapshot performance packages/agent/test/chrome.js, .github/workflows/pull_request.yml	A serial browser test compares snapshot timing with a base source across three page shapes. The workflow fetches the pull request base commit and sets PERF_BASE for pull request events.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Refactor

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Merge Risk: ⚪ Minimal · up to c8adf

The change makes snapshot scope text reads once per snapshot and adds a base-versus-head performance comparison to the tests. No concrete merge-blocking risk remains from this review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main performance change: reading shared scope text once per snapshot.
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 3…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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[coveralls]

coverage: 77.158%. first build — codex/perf-agent-scope-text into master

[Kikobeats]

Snapshot performance

In-page snapshot p50, same Chrome, 1280×800, interleaved with the base commit. A later change to snapshot.js has to stay at or under these base numbers. The agent test fails when a fixture is more than 10% slower and more than 1 ms slower. That band is timer noise. Identical source skips the timing.

Fixture	This PR	Base
Listings	0.9 ms	0.9 ms
Grid	11.8 ms	49.7 ms
Long document	9.2 ms	8.6 ms