chore(agents): Default to running and verifying in the dev environment

[posthog]

This is actually @Twixes here…

Problem

An agent working on a frontend PR in the cloud task sandbox found no node_modules and no flox, and concluded it "couldn't run Storybook", shipping a visual CSS fix with no visual verification. Even though the sandbox can actually allow this and it would be much preferable to show verification.

Changes

Adding three bullets to the Environment section of AGENTS.md:

• Treat the sandbox as a full dev environment
• Default to verifying by running, only conclude "can't" after hitting a specific failure
• For a visual/UX change, actually render it and compare before/after

This is worded as steps to take rather than a strong statement so that this works even on a constrained sandbox.

[github-actions]

🤖 CI report

✅ Bundle size — no change

Uncompressed size of every built .js bundle, compared against the base branch.

Total: 65.15 MiB · no change

No file changed by more than 1000 B.

_{Posted automatically by build-bundle-size-report · uncompressed bytes from dist-report}

✅ Eager graph — within budget

How much code each root ships on the eager path — downloaded and parsed before the surface is interactive. Measured from the esbuild output chunks (post-tree-shake, static imports only); lazy import() / React.lazy chunks are not counted.

Root	Eager (shipped)	Δ vs base	Budget
entry (logged-out pages, app bootstrap) src/index.tsx	1.24 MiB · 22 files	🔺 +491 B (+0.0%)	███░░░░░░░ 27.6% of 4.51 MiB
authenticated shell (every logged-in page) src/scenes/AuthenticatedShell.tsx	8.08 MiB · 3,013 files	🔺 +491 B (+0.0%)	████████░░ 83.2% of 9.71 MiB

🟢 node_modules/monaco-editor/ stays out of src/index.tsx
🟢 src/lib/components/ActivityLog/describers stays out of src/index.tsx
🟢 [object Object] stays out of src/index.tsx
🟢 [object Object] stays out of src/index.tsx
🟢 node_modules/monaco-editor/ stays out of src/scenes/AuthenticatedShell.tsx
🟢 src/lib/components/ActivityLog/describers stays out of src/scenes/AuthenticatedShell.tsx
🟢 [object Object] stays out of src/scenes/AuthenticatedShell.tsx
🟢 [object Object] stays out of src/scenes/AuthenticatedShell.tsx

Largest files eagerly shipped from src/index.tsx

Size	File
126.8 KiB	../node_modules/.pnpm/react-dom@18.3.1_react@18.3.1/node_modules/react-dom/cjs/react-dom.production.min.js
24.6 KiB	../node_modules/.pnpm/buffer@6.0.3/node_modules/buffer/index.js
6.3 KiB	../node_modules/.pnpm/react@18.3.1/node_modules/react/cjs/react.production.min.js
4.5 KiB	../node_modules/.pnpm/@jspm+core@2.1.0/node_modules/@jspm/core/nodelibs/browser/process.js
3.9 KiB	../node_modules/.pnpm/scheduler@0.23.2/node_modules/scheduler/cjs/scheduler.production.min.js
1.4 KiB	../node_modules/.pnpm/base64-js@1.5.1/node_modules/base64-js/index.js
1.3 KiB	src/RootErrorBoundary.tsx
912 B	../node_modules/.pnpm/ieee754@1.2.1/node_modules/ieee754/index.js
789 B	src/scenes/ChunkLoadErrorBoundary.tsx
762 B	src/index.tsx

Largest files eagerly shipped from src/scenes/AuthenticatedShell.tsx

Size	File
281.5 KiB	../node_modules/.pnpm/posthog-js@1.407.3/node_modules/posthog-js/dist/rrweb.js
267.7 KiB	../node_modules/.pnpm/@posthog+icons@0.38.0_react-dom@18.3.1_react@18.3.1__react@18.3.1/node_modules/@posthog/icons/dist/posthog-icons.es.js
234.2 KiB	src/taxonomy/core-filter-definitions-by-group.json
226.4 KiB	../node_modules/.pnpm/posthog-js@1.407.3/node_modules/posthog-js/dist/module.js
154.3 KiB	../node_modules/.pnpm/re2js@0.4.1/node_modules/re2js/build/index.esm.js
126.8 KiB	../node_modules/.pnpm/react-dom@18.3.1_react@18.3.1/node_modules/react-dom/cjs/react-dom.production.min.js
105.1 KiB	src/lib/api.ts
94.0 KiB	../packages/quill/packages/quill/dist/index.js
93.3 KiB	../node_modules/.pnpm/prosemirror-view@1.40.1/node_modules/prosemirror-view/dist/index.js
90.6 KiB	../node_modules/.pnpm/@tiptap+core@3.20.6_@tiptap+pm@3.20.6/node_modules/@tiptap/core/dist/index.js

_{Posted automatically by check-eager-graph · sizes are eager output bytes (shipped, post-tree-shake) from the esbuild metafile · part of #32479}

✅ Toolbar bundle — eager 2.18 MiB within budget

What the toolbar ships to customer pages, measured from the esbuild output (minified, post-tree-shake). The eager set is the entry plus everything statically imported from it — fetched before any feature runs; deferred chunks load lazily. The eager guardrail is 5.72 MiB. Each output file must also stay below 10 MB, where CloudFront stops compressing it. The module boundary is enforced separately by check-toolbar-graph.

Metric	Size	Δ vs base	Budget
Eager (shipped) entry + static imports	2.18 MiB · 17 files	no change	████░░░░░░ 38.2% of 5.72 MiB
Deferred (lazy)	2.07 MiB · 33 files	no change	n/a — loads on demand
Loader dist/toolbar.js	1.1 KiB	no change	█░░░░░░░░░ 5.8% of 19.5 KiB

Largest eagerly-shipped chunks

Size	File
716.4 KiB	dist/toolbar/toolbar-app-V5IF6GYH.css
545.6 KiB	dist/toolbar/chunk-chunk-FXPCABFT.js
484.3 KiB	dist/toolbar/chunk-chunk-6XXSRP4X.js
133.6 KiB	dist/toolbar/chunk-chunk-IPCZ6XI2.js
131.8 KiB	dist/toolbar/chunk-chunk-T5KY5WYR.js
71.0 KiB	dist/toolbar/toolbar-app-QQPRCZD2.js
69.0 KiB	dist/toolbar/chunk-chunk-27JL52RE.js
35.6 KiB	dist/toolbar/chunk-chunk-MA3DSLUQ.js
20.9 KiB	dist/toolbar/chunk-chunk-TJW7UT6L.js
12.2 KiB	dist/toolbar/chunk-chunk-PIK3PADE.js

_{Posted automatically by check-toolbar-size · sizes are toolbar output bytes (shipped, post-tree-shake) from the esbuild metafile}

✅ Dist folder size — 🔺 +1.11 MiB (+0.1%)

Total size of the built frontend/dist folder (all assets), compared against the base branch.

Total: 1360.93 MiB · 🔺 +1.11 MiB (+0.1%)

[posthog]

👋 Visual changes detected for this PR.

Review and approve in PostHog Visual Review

If these changes are unexpected, they may be caused by a flaky test or a broken snapshot on master. Don't approve — rerun the job or wait for a fix.

[posthog]

Folded into #74118 (combined with the artifact-download-URL change), per maintainer request. The AGENTS.md environment guidance now ships there.