Slack messages fail to send intermittently

[chandima]

Slack outbound messages fail intermittently despite valid bot token (verified via curl). 132 failures observed in one day across all message sizes. WebSocket logs show ResetWithoutClosingHandshake errors.

Root cause: HTTP client bug in slack-morphism v2.17 / older tokio-tungstenite.

Fix: Upgrade slack-morphism to v2.19 (#516).

[chandima]

Converting to draft while investigating root cause. Will reopen with complete findings.

[chandima]

Update: Root cause confirmed and fix tested

Fix

Upgraded slack-morphism from v2.17.0 to v2.19.0 (one-line change in Cargo.toml).

What changed upstream (2.17 → 2.19)

• tokio-tungstenite updated to 0.29.0 (WebSocket layer — likely fixes ResetWithoutClosingHandshake)
• signal-hook updated to 0.4.x
• Flexible paging API and new files API methods

Test results with v2.19.0

• Zero send failures across multiple messages (16 bytes to 3.5KB)
• Zero WebSocket errors — no ResetWithoutClosingHandshake observed
• Full worker pipeline tested: arxiv paper review → worker spawned → browser tools → 3,516 byte result delivered via retrigger — all first-try, no retries needed
• Previously: 132 send failures in one day on v2.17.0

Conclusion

The intermittent HTTP client failures were caused by bugs in the older slack-morphism / tokio-tungstenite stack. No application-level retry logic needed — the upgrade alone resolves the issue.

PR incoming.