Two related executor fixes:
1. Spawned child agents previously bypassed the executor model lane hierarchy
and used settings.defaultProvider/defaultModelId directly, ignoring
project-level executionProvider/executionModelId from .fusion/config.json.
Resolve via resolveExecutorModelPair() so children honor the same
precedence as the parent executor.
2. Pre-merge workflow step AI calls now have a wall-clock timeout
(settings.workflowStepTimeoutMs, default 6 min) and fall back to the
configured validatorFallback / fallback model on timeout. The 20-min
stuck-detector kill loop was the only escape hatch when a provider's
streaming API hung mid-response, and the kill triggered a same-provider
retry — guaranteeing repeat hangs. The runner now races the prompt against
a timeout; on timeout it disposes the session, logs a clear entry, and
re-runs the step once with a distinct fallback provider/model. If neither
completes (or no fallback is configured), the step returns a normal
failure that flows into the existing handleWorkflowStepFailure retry path.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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