Add stale-if-error to app shell Cache-Control

[Celant]

Description:

Adds stale-if-error=86400 to the Cache-Control header set on the rendered app shell (/) in src/server/RenderHtml.ts. This lets shared caches (CloudFlare, nginx proxy_cache) keep serving the last good index.html for up to 24h if origin returns a 5xx, alongside the existing stale-while-revalidate window.

Pairs with enabling HTML caching for the / route on CloudFlare in "respect origin headers" mode — it already honors s-maxage (5 min edge TTL) and stale-while-revalidate; this just extends the same safety net to origin-error cases.

No behavior change for successful responses; browsers still revalidate every load via max-age=0.

Please complete the following:

• I have added screenshots for all UI updates
• I process any text displayed to the user through translateText() and I've added it to the en.json file
• I have added relevant tests to the test directory
• I confirm I have thoroughly tested these changes and take full responsibility for any bugs introduced

Please put your Discord username so you can be contacted if a bug or regression is found:

jish

[coderabbitai]

Walkthrough

The PR updates the app shell Cache-Control header to include stale-if-error=86400, allowing stale content to be served for up to 24 hours when errors occur, and updates the test expectation accordingly.

Changes

App shell cache control header update

Layer / File(s)	Summary
App shell cache control header and test src/server/RenderHtml.ts, tests/server/RenderHtml.test.ts	APP_SHELL_CACHE_CONTROL now includes stale-if-error=86400; the test expectation for setAppShellCacheHeaders was updated to match the new header value.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

When headers whisper through the net,
A little grace for outages set,
Stale but steady, twenty-four bright,
Serving pages through the night. ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Add stale-if-error to app shell Cache-Control' clearly and concisely summarizes the main change in the changeset.
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.
Description check	✅ Passed	The pull request description clearly explains the change: adding stale-if-error=86400 to Cache-Control header for the app shell, its purpose for shared caches during origin errors, and how it pairs with CloudFlare configuration.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/server/RenderHtml.ts`:
- Line 10: The test expectation in tests/server/RenderHtml.test.ts must be
updated to match the new Cache-Control header emitted by RenderHtml (the string
in RenderHtml.ts was changed to "public, max-age=0, s-maxage=300,
stale-while-revalidate=86400, stale-if-error=86400"); open
tests/server/RenderHtml.test.ts and replace the old expected Cache-Control value
with the new full string so the assertion for the Cache-Control header (around
the assertion block at lines ~52-66) matches the value produced by
RenderHtml.renderHtml / the Cache-Control constant.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: ace019fd-798f-441d-90e5-135e9f904005

📥 Commits

Reviewing files that changed from the base of the PR and between 2b45813 and 25ae4ae.

📒 Files selected for processing (1)

• src/server/RenderHtml.ts