fix(website): isolate Lazy fallback-discovery from page cache state

[igoramf]

Problem

Storefront home pages (e.g. www.farmrio.com.br/) were served with
Cache-Control: no-store while PLP/PDP cached normally
(public,max-age=180,stale-while-revalidate=3600). CDN full-page cache
was fully disabled on the highest-traffic page.

Root cause

website/sections/Rendering/Lazy.tsx defers rendering of its child
section, but its loader resolves that child once up front just to
read its LoadingFallback and metadata:

const resolvedSection = await resolveSection({}, { ... });

The engine resolves a deferred value with { ...context, ...partialCtx }
(engine/core/mod.ts). Passing {} means the child's whole resolve
subtree runs against the parent page's request state — its vary,
flags, response and bag. So any deferred section whose loader is
no-store (or returns a null cache key) sets ctx.vary.shouldCache = false on the page (blocks/loader.ts), and the middleware then writes
no-store for the entire page (runtime/middleware.ts,
applyPageCacheDecision).

A home with ~70 Lazy sections only needs one of them to touch a
per-user loader (cart, weather, session, …) for the whole page to become
uncacheable — even though that section is deferred and its real render
happens later in a separate partial request.

Fix

Resolve the fallback against an isolated request state
(newIsolatedRequestState()), covering exactly the four keys the engine
threads as request state (bag, flags, response, vary — see
runtime/utils.ts). Speculative mutations during fallback discovery are
discarded. The eager partial still re-resolves the section with the real
request state, so personalized/deferred sections stay personalized.

Tests

website/utils/isolatedRequestState.test.ts asserts two isolated states
don't share vary/flags/response/bag and that side effects on one
don't leak to the other. deno test passes; deno check clean on both
changed files.

🤖 Generated with Claude Code

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Summary by cubic

Fixes a bug where deferred sections in Lazy could disable full-page caching by leaking per-user loader mutations into the page state. Fallback discovery now runs in an isolated request state, restoring CDN caching on homepages while keeping personalization intact.

• Bug Fixes
  • Resolve Lazy fallback with newIsolatedRequestState() so bag, flags, response, and vary mutations don’t affect the page.
  • Keep the eager partial re-resolving with the real request state to preserve personalization.
  • Added tests to ensure no leakage between isolated and real request states.

^{Written for commit 0bb69c2. Summary will update on new commits.}

Summary by CodeRabbit

• Bug Fixes

  • Improved lazy-loaded section handling to prevent speculative resolution from affecting the parent page’s caching, response headers, or feature state.
  • Preserved existing eager and lazy rendering behavior.

• Tests

  • Added coverage confirming isolated request state remains independent across separate resolutions.

[github-actions]

Tagging Options

Should a new tag be published when this PR is merged?

• 👍 for Patch 0.159.8 update
• 🎉 for Minor 0.160.0 update
• 🚀 for Major 1.0.0 update

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 13e4c68f-09e1-4fab-94b2-4057744c417d

📥 Commits

Reviewing files that changed from the base of the PR and between a0a57a1 and 0bb69c2.

📒 Files selected for processing (3)

• website/sections/Rendering/Lazy.tsx
• website/utils/isolatedRequestState.test.ts
• website/utils/isolatedRequestState.ts

---

📝 Walkthrough

Walkthrough

Changes

Lazy resolution isolation

Layer / File(s)	Summary
Isolated request-state factory and validation website/utils/isolatedRequestState.ts, website/utils/isolatedRequestState.test.ts	Adds newIsolatedRequestState with independent resolver state for bags, flags, response headers, and cache-vary tracking, plus tests for defaults and non-aliasing.
Deferred loader integration website/sections/Rendering/Lazy.tsx	The lazy loader resolves deferred sections with isolated request state after aborting the original controller.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• deco-cx/apps#1369: Also modifies deferred section resolution in Lazy.tsx, including URL-based forcing and metadata guards.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description does not follow the required template and is missing the Issue Link, Loom Video, and Demonstration Link sections.	Add the required template sections: What is this Contribution About?, Issue Link, Loom Video, and Demonstration Link, with the relevant details and links.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main change: isolating Lazy fallback discovery from page cache state.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/lazy-cache-state-isolation

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[cubic-dev-ai]

No issues found across 3 files

_{Re-trigger cubic}