Audit all agent-facing parameter structs for silent unknown-field discard #1816

Overview

Generalize the coreValues fix. Any agent-facing deserialization target without deny_unknown_fields turns a model typo into silent data loss plus a misleading downstream error.

Problem Statement

The coreValues casing bug cost a full spike investigation to localize, purely because the failure surfaced two layers from its cause: the key was dropped silently, then validation failed with a message about a different thing.

Every Deserialize struct reachable from a tool call has this property. With a small local model that will occasionally misspell a key, silent discard is the wrong default everywhere.

Evidence

• grep -rn "deny_unknown_fields" packages/agent/src packages/core/src returns zero hits across both crates
• packages/core/src/schema/mod.rs:139 CreateSchemaParams and :167 AdditionalConstraints — neither sets it
• The coreValues incident: prose taught the wrong casing, the key was discarded without error, and validation reported "enum has no values"

Acceptance Criteria

• Every struct deserialized from tool-call arguments carries deny_unknown_fields
• Rejection errors name the offending field and list the accepted fields, so the model can self-correct from the error text
• A test per tool asserts an unknown argument is rejected rather than ignored

Architecture Impact

Converts a silent-corruption class into a loud-failure class. An informative rejection also doubles as a repair signal the model can act on — consistent with ADR-064 rule 4, where tool results carry facts the model can use rather than prose it must interpret.

Depends on the coreValues fix landing the pattern first.