fix: always trigger serverless ended early error

[MasterPtato]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[railway-app]

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[MasterPtato]

• fix: always trigger serverless ended early error #4320 👈 (View in Graphite)
• fix: remove useless config params #4319
• fix: add serverless leak fix oneoff #4318
• chore: add log for runners with no alloc idx #4316
• fix(ups): upgrade nats, fix chunking, add chunking tests #4315
• chore: fix tests #4314
• fix: various serverless bug fixes #4313
• fix(guard, runner): enforce http body size and ws msg size #4252
• fix(pegboard): add threshold parameters to runner protocol metadata #4247
• chore: get docker compose working again #4246
• fix(epoxy): make quorum sizes match paper #4234
• fix(rivetkit): stall stop handler until start completes #4192
• main

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[claude]

PR Review

Summary

This PR makes three changes:

1. Always report ServerlessStreamEndedEarly error when an SSE stream ends unexpectedly in outbound_req_inner, regardless of whether the runner had initialized.
2. Config schema cleanup: alphabetically reorders runner_lost_threshold relative to runner_max_response_payload_body_size (renamed from runner_http_max_response_body_size in the parent PR), and removes the stale "Default is 10 seconds." note from serverless_drain_grace_period.
3. Frontend error message improvement: replaces a vague "Connection terminated unexpectedly" with an actionable message pointing users to configure the request lifespan.

---

Core Logic Change (conn.rs)

The fix is correct. The stream_handler future in outbound_req_inner runs inside a tokio::select! alongside time-based drain and signal paths. The only time StreamEnded fires inside stream_handler is when the server-side SSE stream closes before the drain path takes over, which is always unexpected.

Before: Only reported an error if runner_id.is_none() (runner never initialized). A runner that initialized and then had its stream cut short would silently return Ok(OutboundReqOutput::Continue) with no error recorded.

After: Always reports the error. This is sound because the normal shutdown path goes through finish_non_critical_draining, which separately handles StreamEnded as an expected event (Err(sse::Error::StreamEnded) => break). There is no legitimate path where StreamEnded in the main stream handler is benign.

---

Feedback

Minor — Incomplete PR description: The checklist is untouched and no test steps are described. A brief note about how the issue was reproduced would help reviewers and future bisectors.

Minor — No test coverage: There is no automated test for the scenario where StreamEnded fires after a runner initializes. It would be worth adding a regression test if the setup allows simulating a premature stream closure.

Nit — Config schema field rename: runner_http_max_response_body_size to runner_max_response_payload_body_size is a breaking config change for anyone with the old key set. Worth confirming whether a deprecation path is needed, or if this is fine to change directly given it is part of the parent PR.

---

Verdict

The behavioral fix is correct and the improved error message is genuinely helpful. The changes are small, focused, and low-risk. No blocking issues.

[pkg-pr-new]

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commit: 65b8a35