fix: draftMode() must mark dynamic usage to prevent caching

[NathanDrake2406]

Summary

• draftMode() reads the __prerender_bypass cookie (request-specific data) but did not call markDynamicUsage(), unlike headers() and cookies()
• This means a Server Component branching on draftMode().isEnabled could have its output cached by ISR, serving draft content to regular users or stale content to draft users
• Added the missing markDynamicUsage() call and a test verifying the behavior

Test plan

• New test: draftMode() marks dynamic usage so the render is uncacheable — calls draftMode() within a headers context and asserts consumeDynamicUsage() returns true
• All existing draft-mode tests pass (8/8)

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/vinext@369

commit: 0c120ec

[james-elicx]

/bigbonk review this pr

[ask-bonk]

Clean, correct fix. draftMode() reads the __prerender_bypass cookie (request-specific data) and was the only dynamic request API in the headers shim that didn't call markDynamicUsage(). Without this, ISR could cache a response that branched on draftMode().isEnabled, serving draft content to regular users or vice versa.

Verified that the fix is consistent with the existing pattern:

• headers() — calls markDynamicUsage() (line 276)
• cookies() — calls markDynamicUsage() (line 294)
• connection() in server.ts — calls markDynamicUsage() (line 459)
• noStore() in cache.ts — calls _markDynamic() (line 365)
• draftMode() — now calls markDynamicUsage() (line 362) ✓

Placement is correct — it's called before _getState() reads the cookie, matching the throwIfInsideCacheScope → markDynamicUsage → read-state ordering used by headers() and cookies().

Test is well-structured: sets up ALS context, resets prior dynamic usage, calls draftMode(), and asserts the flag is set. Good use of the existing runWithHeadersContext / consumeDynamicUsage test utilities.

[ask-bonk]

Approved. This is a correct one-line fix that closes a real caching bug. draftMode() was the only dynamic request API that didn't call markDynamicUsage(), meaning ISR could incorrectly cache responses that branched on draft mode state. The fix is consistent with how headers(), cookies(), connection(), and noStore() all mark dynamic usage, and the test properly verifies the behavior.

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