Two new Mantle shims, auto-installed alongside the existing pair:
- Opt out of the fine-grained-tool-streaming beta. Under it, an
output-token cutoff mid-tool_use ends the stream without
content_block_stop; fast-agent raises "Streaming completed but tool
call never finished" and burns its retry ladder against the same
wall (the observed ~700s Alan revise_workspace_file failures on
Taurus).
- Clamp default maxTokens to Mantle's observed 20 000-token server
ceiling, so the model stops gracefully (proper block close +
stop_reason=max_tokens) instead of being cut off by the gateway.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Introduce `model_capabilities.mantle` flag that installs a provider-specific
override in fast-agent's `ModelDatabase._PROVIDER_MODEL_OVERRIDES` to strip
features the AWS Bedrock Mantle endpoint rejects (beta headers, extended
thinking, task budgets, web tools, prompt caching).
Without this override, fast-agent sends default beta headers and `thinking`
parameters for modern Claude models that Mantle rejects with a misleading
404 "model does not exist" error.
