Add isLoop helper to functions:init scaffolded handler

[etbyrd]

Summary

A deployed Primitive Function receives catch-all inbound for the managed *.primitive.email subdomain. That stream includes bounces and auto-replies generated by the handler's own outbound traffic. Without a loop guard the handler can respond to its own bounces and create a fan-out loop.

The scaffolded handler now exports a small isLoop(event) helper. The fetch dispatcher calls it right after the event-type check and returns early with Response.json({ skipped: 'loop' }) when it returns true.

Default predicate:

• From on any *.primitive.email address (covers the catch-all managed subdomain, simple self-reply, and bounces from mailer-daemon@*.primitive.email).
• From matching the configured REPLY_FROM (covers handlers whose sender is on a non-managed domain).

Comparisons are case-insensitive substring matches so a display-name form (Alice <alice@example.com>) works without parsing the bracketed address.

The default is intentionally small. The comment block above the helper lists common extensions so the next author knows where to add sophistication:

• Match the org's signup / account-owner email.
• Honor RFC 3834 Auto-Submitted headers and Precedence: bulk / List-Unsubscribe.
• Track Message-ID / In-Reply-To chains to break ping-pong loops between two cooperating handlers on different domains.

Test plan

• pnpm --filter @primitivedotdev/cli lint
• pnpm --filter @primitivedotdev/cli typecheck
• pnpm --filter @primitivedotdev/cli test functions-init (27 tests pass; new tests cover the helper export, the dispatcher call site, the two predicate arms, and the extension-point comment)

[greptile-apps]

Greptile Summary

This PR replaces the scaffolded handler's inline self-reply guard with a named, exported isLoop(event) helper and updates the fetch dispatcher to call it after the event-type check, returning early with { skipped: 'loop' } on a match.

• The helper's two predicate arms — .primitive.email suffix check and case-insensitive REPLY_FROM substring check — are well-documented, including explicit acknowledgment of the substring false-positive trade-off and a comment block enumerating extension points (RFC 3834, Message-ID chains, signup-email matching).
• Four new tests cover the helper export, dispatcher call site, both predicate arms, and the extension-point comment; the previous single test is cleanly replaced.

Confidence Score: 5/5

Safe to merge — the change is additive, scoped entirely to the scaffolded handler template, and ships with full test coverage.

The predicate logic is straightforward and its trade-offs (substring false positives, empty-From passthrough) are explicitly documented in both the comment block and the PR description, leaving nothing implicit for the next author. The dispatcher integration is minimal and the existing catch-all error handler remains intact.

No files require special attention.

Important Files Changed

Filename	Overview
cli-node/src/oclif/commands/functions-init.ts	Adds isLoop helper and dispatcher call site to the scaffolded handler template; refactors the previous single-line self-reply guard into a documented, extensible predicate with two arms (.primitive.email suffix and case-insensitive REPLY_FROM substring).
cli-node/tests/oclif/functions-init.test.ts	Replaces the single self-reply test with four targeted assertions covering: helper export + dispatcher call, both predicate arms with .toLowerCase() and .includes(), and the extension-point comment block; all structured to test the rendered template string.

_{Reviews (3): Last reviewed commit: "Merge branch 'main' into functions-init-..." | Re-trigger Greptile}