Fix email reply References threading

[plarson]

Summary

• Preserve inbound email References when sending gateway replies
• Append the current inbound Message-ID to the outbound References chain
• Cover the behavior with focused email threading header tests

Test

• uv run --with pytest pytest -q tests/test_email_threading_headers.py
• python -m py_compile plugins/platforms/email/adapter.py tests/test_email_threading_headers.py

[Copilot]

Pull request overview

This PR improves email reply threading in the gateway’s Email platform adapter by carrying forward inbound References headers into outbound replies and extending the References chain with the message being replied to, with new focused tests to validate the behavior.

Changes:

• Capture inbound References in _fetch_new_messages() and persist it into _thread_context during dispatch.
• Build outbound References by combining stored inbound References with the current Message-ID being replied to (for plain and attachment sends).
• Add focused tests asserting In-Reply-To and References behavior for replies with/without prior References.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
plugins/platforms/email/adapter.py	Stores inbound References and uses it to build outbound reply threading headers.
tests/test_email_threading_headers.py	Adds targeted tests validating outbound In-Reply-To/References header construction.

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[alt-glitch]

This was generated by AI during triage.

Email-threading cluster: this PR is the narrow outbound References-chain fix. Broader OPEN siblings cover overlapping ground — #27508 (References-root Message-ID as thread_id + outbound References, most standards-complete), #23999 (Gmail Message-ID/In-Reply-To/References preservation), #11185 (rekey thread_context by root Message-ID). Related, not duplicate (subset of #27508). Flagging the cluster for a maintainer to pick the canonical approach.

[plarson]

Addressed the review feedback about re-emitting inbound References verbatim.

Update:

• Added helper logic to unfold/sanitize inbound References values before reuse.
• Deduplicates message IDs while preserving order.
• Uses the helper in all three outbound send paths.
• Added regression coverage for folded References headers and duplicate current message IDs.

Verification:

• uv run --with pytest pytest -q tests/test_email_threading_headers.py → 3 passed
• python -m py_compile plugins/platforms/email/adapter.py tests/test_email_threading_headers.py
• git diff --check

[teknium1]

Thank you for addressing the folded-header and duplicate-ID feedback; the new helper in plugins/platforms/email/adapter.py:71-108 is a clear improvement over re-emitting inbound header text.

Problems

• plugins/platforms/email/adapter.py:881 adds references to context that is still keyed only by sender_addr. Current main reads that context by recipient address in all three send paths (:933, :1047, :1127). If one sender has two active email threads, the later inbound message overwrites the earlier thread's References chain. The gateway passes the individual reply anchor (gateway/platforms/base.py:5028-5033), but _send_email combines it with that overwritten context.

Suggested changes

• Carry a stable email-thread key through dispatch and reply delivery, then key context by that value; add a two-threads/same-sender regression test.
• Add attachment-path coverage for the two additional changed send methods.

Automated hermes-sweeper review.

[teknium1]

This value is still stored under sender_addr, while every send path later retrieves context by recipient address. A second, unrelated thread from the same sender overwrites this References chain before the first thread's response is sent. Please key/route the context by a stable email-thread identity and add a same-sender/two-threads regression.