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Why repair exists

Status: Mostly shipped. Schema-based tool-call repair runs in the agent loop before validation, including parse leniency, ambiguity refusal, alias/typo key rename, and strict unknown-key rejection. Per-model posture, telemetry, and per-shape backends remain Spec — not shipped — see The repair cascade.

OSS backends malform tool-call arguments in model-specific ways: stringified JSON, truncated JSON, trailing commas, ambiguous field names. Each malformation, left alone, costs a whole turn.

Repair makes recoverable calls land on the first attempt. It coerces malformed-but-clear JSON into an object and re-validates; when a call genuinely cannot be made valid, it fails loud back to the model with coaching, never dispatched as garbage.

The lever

Edit format / first-attempt success. Repair is the safety net under every schema-bearing tool call, most importantly the edit path, where a malformed call is a failed edit.

Shipped behavior

  • Seam: argument repair runs in the agent loop, before argument validation.
  • Fix-if-clear: trailing commas, parse sentinels (__parseError / __rawJson), stringified JSON objects.
  • Refuse-if-ambiguous: missing required strings with multiple plausible sources → unrepairable (no invent).
  • Alias/typo rename: unknown keys that clearly alias a declared property are renamed; refuses on genuine ambiguity instead of guessing.
  • Strict unknown-key rejection: additionalProperties: false schemas refuse leftover unrecognized keys after alias resolution.
  • Bounded: inputs over 1 MiB refuse repair.
  • Disable: VEYYON_REPAIR_DISABLE=1 or per-model harness.profiles with repair: false.

Not shipped yet

  • Per-tool shape tables beyond the generic alias/strict rules
  • Per-(model,tool,shape) telemetry store
  • Per-model posture knobs

The shipped rule cascade and its conformance suite live in the TypeScript repair module (packages/coding-agent/src/repair/schema-repair.ts, tested by packages/coding-agent/test/repair/schema-repair.test.ts) at the tool-dispatch seam — this stays a TS module, not a separate Rust crate.

See The repair cascade, Per-model posture, and Soundness and telemetry for the target design. For the shipped edit engine, see The hashline edit engine.