refactor(cdp): rename emailAssets to messageAssets

[dmarchuk]

Problem

The field that carries captured message assets on an invocation result is called emailAssets, but since #74555 it also carries push notification rows. The name now says the wrong thing at every call site that touches push.

This is the rename from #75801, which was reviewed and approved there. That PR was stacked on #75800 and merged into its base branch rather than into master, so the rename never reached master. #75800 is being closed because its own change turned out to be unnecessary — a test push send records no metrics, logs or assets, since the test endpoint returns them inline and discards the result. This PR carries the rename on its own.

Changes

emailAssets → messageAssets across nodejs/src. Field name only, no behavior change.

15 of the 17 files are byte-identical to the version reviewed in #75801. The two that differ are the push notification service and its test, and they differ only by the isTest guard that belonged to #75800 and is deliberately not included here.

How did you test this code?

• 0 occurrences of emailAssets remain anywhere in the repo (not just nodejs/src); 60 of messageAssets.
• tsc --noEmit reports no errors beyond the pre-existing @posthog/replay-anonymizer module-resolution ones from an unbuilt local package.
• Manually end-to-end on the renamed code: one trigger through a workflow that sends both channels captured 3 push rows and 1 email row in message_assets, all sent, with correct recipients, subjects and HTML. So the collector and the producers still agree on the field after the rename.

No test added: a rename with no behavior change has no regression to catch that the type checker doesn't.

Automatic notifications

None.

Docs update

Not needed. Internal field name, no user-facing surface.

🤖 Agent context

Written with Claude Code. Reconstructed by applying the rename directly to master rather than cherry-picking #75801's commit, because that commit's diff was computed against #75800's guard and would not apply cleanly. The result was then diffed against the reviewed version file by file to confirm equivalence.

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[dmarchuk]

Duplicate with #75801