Add Cloudflare Actions build regression coverage

[swaggysnippets]

What changed

• adds a Cloudflare fixture with an Astro Action
• verifies two consecutive builds succeed while reusing the warm Vite dependency cache
• removes the broad three-attempt fixture build retry that masked stale prebundle failures

Why

Astro issue #16933 reported Cloudflare builds failing when src/actions/index.ts was present because dependency optimization could observe a stale prebundle. The runtime startup change in #16961 addressed the production failure; this PR adds deterministic regression coverage so that behavior remains protected and optimizer races fail visibly instead of being hidden by retries.

Validation

• Cloudflare integration build passes
• optimizer-sensitive test subset: 11 passed
• full Cloudflare adapter suite: 263 passed, 1 skipped, 0 failed
• Biome and Prettier checks pass
• lockfile frozen install check passes

[changeset-bot]

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Latest commit: f7f3caa

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[fkatsuhiro]

@swaggysnippets san
Thank you for your PR!
But it seems there aren't changeset file. Could you add in this PR? To explain user what we changed. Thank you.

[fkatsuhiro]

@swaggysnippets san Thank you for your PR! But it seems there aren't changeset file. Could you add in this PR? To explain user what we changed. Thank you.

Oh, sorry. This PR for improve testing. I approgise my missunderstanding...

[alexanderniebuhr]

@swaggysnippets thanks for your PR, which discovered a real missing test. However I have reviewed it and found that it doesn't technically solves your described gap. I still want to use this PR to get this merged, so I updated the branch for you.

What changed

• Restored buildWithRetry in test-utils.ts (byte-identical to main). The stale-prebundle race it guards was never root-caused or fixed — Build fails when using src/actions/index.ts #16933 was closed "unable to fix" — and all 49 Cloudflare test files run serially in one process with no CI-level retry, so deleting it just converts a known flake into red 30-minute CI legs.
• Deleted the actions-build fixture, its test, and its lockfile entry — it provided no coverage (details below) and duplicated existing fixtures (sessions already builds Actions on workerd; prerender-node-env already covers Actions with prerenderEnvironment: 'node').
• Added typegen-phase.test.ts: it invokes the adapter's astro:config:setup hook directly for build, sync, and dev, and asserts the two things Skip Cloudflare runtime startup during type generation #16961 actually changed — during build/sync the Cloudflare Vite plugins have configureServer stripped (no workerd boot during type generation) and configEnvironment returns { optimizeDeps: { noDiscovery: true, include: [] } } for every environment; in dev both stay enabled and the include list still prebundles the Actions server entrypoints. Six tests, ~6 ms, no build, no server, no flake.