feat(combo): add per-model timeout for faster combo fallback

[berthojoris]

Summary

Adds configurable per-model timeout to combo fallback, so when a model is busy or timing out, the combo falls back to the next model faster instead of waiting the full 60s fetch connect timeout.

Changes

1. Per-combo timeout config (timeoutMs in comboStrategies)

• src/sse/handlers/chat.js — Reads timeoutMs from comboStrategies (per-combo), falls back to global COMBO_MODEL_TIMEOUT_MS env var, then to 0 (disabled). Passes it to handleComboChat().

2. Promise.race timeout in handleComboChat()

• open-sse/services/combo.js — Accepts comboTimeoutMs parameter. When > 0, wraps each model call in Promise.race with a timer. On timeout, the error carries isComboTimeout: true — the catch block skips setting lastError so the final error message stays accurate. Fallback continues to the next model.

3. UI input on combo dashboard

• src/app/(dashboard)/dashboard/combos/page.js — Adds a small timeout input (in seconds) next to the strategy selector for fallback/round-robin combos. Fusion combos use their own panel timeout and are excluded. Updated pruning logic to preserve timeoutMs in handleSetComboStrategy.

4. Global env override

• open-sse/config/runtimeConfig.js — Adds COMBO_MODEL_TIMEOUT_MS env-controlled default (0 = disabled, use existing 60s fetch connect timeout).

How it works

User sets 15s timeout in dashboard
  -> comboStrategies["my-combo"].timeoutMs = 15000
    -> combo.js wraps each model with Promise.race(handleSingleModel, timer 15s)
      -> 15s without response -> error.isComboTimeout = true
        -> logs warning, falls to next model

Files changed

• open-sse/services/combo.js
• src/sse/handlers/chat.js
• open-sse/config/runtimeConfig.js
• src/app/(dashboard)/dashboard/combos/page.js

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