Web UI: assistant messages re-render as one-fragment-per-line after tab switch/reload for non-Kimi (OpenAI-compatible) providers

[chenxupeng1990-eng]

Describe the bug
In the web UI, assistant messages in sessions using a custom OpenAI-compatible provider render correctly while streaming, but after any remount (browser tab switch and back, page reload, or reopening the session) they re-render as one stream delta per line — a narrow vertical strip. The same session renders correctly with Kimi providers.

Version
Kimi Code CLI 0.36.1 (web UI), macOS. Also present on 0.29.1; persists after upgrading.

To Reproduce

1. Configure a custom OpenAI-compatible provider (tested: Aliyun DashScope, model qwen3.8-max)
2. Start a web UI session with that model and get a reply
3. While streaming / right after: reply renders correctly (full-width markdown)
4. Switch to another browser tab and back (or reload / reopen the session)
5. The reply re-renders as one delta fragment per line in a narrow vertical column; stays broken forever after

Expected behavior
Streamed text deltas are coalesced into a single markdown message block on replay, exactly as with Kimi providers.

Actual behavior
Each streamed text part renders as an independent block/line on replay.

Evidence / root-cause hint

• Session wire.jsonl stores the reply as many tiny text parts (some as short as 3 chars) for BOTH Kimi and custom providers — data is intact; concatenating the parts yields the full text.
• The live streaming path coalesces deltas in memory for all providers; the replay path (tab-return remount, reload, history) re-renders from stored parts without coalescing for non-Kimi providers.
• TUI/terminal rendering is unaffected.
• Not fixed by page refresh or by upgrading 0.29.1 → 0.36.1.

Screenshots of both states (correct live render, broken replay) available on request.

[chenxupeng1990-eng]

Update: this is fixed in 0.36.1. My earlier note that 0.36.1 still reproduced it was invalid — I was unknowingly testing against a leftover 0.29.1 server process (the desktop-managed binary shadowed the upgraded one on PATH). Against a genuine 0.36.1 server, both live streaming and replay (tab switch / reload) render correctly for custom OpenAI-compatible providers. The bug as described applies to ≤0.29.1. Sorry for the noise, and thanks for the fix.