Bounded Tool Output

• Status: Todo
• Kind: Feature
• Authors: Jean Mertz git@jeanmertz.com
• Date: 2026-09-30
• Implements: 115
• Label: type=tracking

Tracking ticket for RFD 115.

Implementation plan

• Add config types for size_threshold: Introduces SizeThreshold ("unlimited" or ByteSize), adds size_threshold to ToolsDefaultsConfig and ToolConfig with the standard config trait impls, a resolver on ToolConfigWithDefaults, and a validator rejecting values below "1KB". Pure config change with no behavior impact; mergeable on its own.
• Let the Record barrier carry replacement content: Extends the Record barrier's reply to carry replacement content, has the execution service deliver it, and has the Host send it when a review is replaced. Covered by a service test (replacement delivered to the MCP caller) and an executor test (unattended call with a replaced review completes without a delivery mismatch); mergeable alone and a dependency for phases 3 and 4.
• Apply the configurable per-tool cap: Adds cap_review and applies it where execute_with_prompting assembles ExecutionResult::reviews. Verified by two turn-loop integration tests (oversized result under Unattended and under Edit) asserting the persisted response is capped within threshold and the correct notice is printed; depends on phases 1 and 2.
• Enforce the batch-wide ceiling: Adds MAX_TOOL_RESPONSE_BATCH_BYTES in commit_tool_responses, truncating the largest responses first across merged reviews and emitting a notice per truncated tool. Tested with a single response exceeding the budget under size_threshold = "unlimited" and multiple individually-small responses that exceed the budget together; depends on phase 2.
• Raise tool-local output caps: Drops or raises MAX_EXPANDED_BYTES in cargo_expand so the new central size_threshold becomes the binding limit for that tool. Small change, only meaningful after phase 3 lands.
• Document the new behavior: Corrects the InlineResults doc comment that incorrectly promises full delivery to the assistant, and documents size_threshold in docs/configuration.md.