Tool-call repair
Models often emit tool arguments that are almost valid JSON or almost match the tool schema: stringified objects, trailing commas, truncated payloads, or misnamed fields. Without a repair step those calls fail validation and cost a full turn.
Repair runs in the agent loop before argument validation. Clear malformations are coerced into a schema-valid object; ambiguous cases are rejected and returned to the model as an error tool result (no dispatch).
Behavior
| Step | What it does |
|---|---|
| Seam | Runs at tool dispatch, before schema validation |
| Fix-if-clear | Trailing commas, parse sentinels (__parseError / __rawJson), stringified JSON objects |
| Leaked markup | A string value holding </parameter><parameter name="k"> markup is split into its own arguments when every leaked name is declared (or i), new, and named once |
| Refuse-if-ambiguous | Missing required strings with multiple plausible sources → unrepairable |
| Alias / typo rename | Unknown keys that map unambiguously to a declared property are renamed; ambiguous renames are rejected |
| Strict unknown keys | Schemas with additionalProperties: false reject leftover keys after alias resolution |
| Tool-specific | task prose escaped twice is decoded; a yield result sent as a JSON string is parsed. Listed in TOOL_ARGUMENT_REPAIRS |
| Size bound | Inputs over 1,048,576 UTF-16 code units are not repaired |
| Disable | VEYYON_REPAIR_DISABLE=1, or per-model harness.profiles with repair: false; both turn off tool-specific repairs too |
Implementation: packages/coding-agent/src/tools/core/repair/schema-repair.ts, with tool-specific repairs in packages/coding-agent/src/tools/core/repair/tool-repairs.ts
Tests: packages/coding-agent/test/edit/schema-repair.test.ts, packages/coding-agent/test/tools/a-tool-specific-argument-repair-reaches-approval-and-the-tool-as-one-set-of-arguments.test.ts
Related
- The repair cascade: ordered rules
- Per-model posture: harness profiles
- Soundness and telemetry
- The hashline edit engine: edit path (separate from argument repair)