defineHarnessHook

Purpose and behavior

Define control code that runs at one point of the built-in harness loop: session-start, before-model, after-model, before-tool, after-tool or stop. Unlike observers, a hook can add instructions, deny or rewrite a tool call, replace its result or refuse to stop; an exception from a hook fails the turn.

Complete example and detailed rules.

Parameters and properties

• optionsRequired
  HarnessHookOptions<Phase>
  Loop phase, optional name and control function of the hook.
• options.onRequired
  Phase
  Loop point where the hook runs.
• options.nameOptional
  string | undefined
  Name for diagnostics, default the phase name.
• options.runRequired
  (input: HarnessHookInput<Phase>) => HarnessHookResult<Phase> | Promise<HarnessHookResult<Phase>>
  Control function for this phase. Hooks of a phase run in declaration order; an exception fails the turn, and an invalid decision fails it with code configuration.

Returns

HarnessHook<Phase>

Signature

export declare function defineHarnessHook<Phase extends HarnessHookPhase>(
  options: HarnessHookOptions<Phase>,
): HarnessHook<Phase>;

Related contracts

• HarnessHook
• HarnessHookOptions
• HarnessHookPhase