vercel/ai · error · HarnessBridgeCapabilityUnsupportedError

ACP permission mapping for

Error message

ACP permission mapping for ${JSON.stringify(permissionMode)} assigns boolean value ${JSON.stringify(target.value)} to select session configuration ${JSON.stringify(target.configId)}.

What it means

Mirror of the boolean case: the mapped permission target assigns a boolean value to a session config option the agent advertised as a 'select' type (which expects one of a fixed set of string values). validateTarget throws this unsupported error before sending the invalid value to the agent.

Solutions

Change the mapping value to one of the select option's allowed string values.
Check the agent's advertised configOptions/options to see the valid choices.
If the option should be boolean, correct the agent or the configId in the mapping.

Example fix

// before
{ type: 'config', configId: 'approval', value: true }
// after
{ type: 'config', configId: 'approval', value: 'auto-approve' }

Defensive patterns

Strategy: validation

Validate before calling

const opt = sessionConfiguration.configOptions?.find(o => o.id === target.configId);
if (opt && opt.type !== 'boolean' && typeof target.value !== 'string') {
  throw new Error(`config ${target.configId} (select) expects a string value`);
}

Type guard

const isSelectConfigValue = (opt: ConfigOption | undefined, value: unknown): value is string =>
  opt != null && opt.type !== 'boolean' && typeof value === 'string';

Prevention

Only use boolean values for options explicitly typed 'boolean'.
Consult the agent's advertised option choices when authoring mappings.
Add a unit test validating every mapping against a fixture session configuration.

When it happens

Trigger: configureACPPermissionMode resolves to a config target { configId, value: true|false } while configOption.type is 'select' (i.e. not boolean), so the code requires typeof value === 'string'.

Common situations: Mapping reused across agents where an option changed from boolean to a select with 'on'/'off' choices; authoring a mapping from a boolean example against a select-based agent.

Related errors

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/72653a30bcd07d48. Report an issue: GitHub.

Appendix: source

Thrown at packages/harness-acp/src/v1/bridge/permission-mode.ts:126

      message:
        `ACP permission mapping for ${JSON.stringify(permissionMode)} requires session configuration ` +
        `${JSON.stringify(target.configId)}, but the agent advertised ` +
        `${formatChoices({ values: availableConfigIds })}.`,
    });
  }
  if (configOption.type === 'boolean') {
    if (typeof target.value !== 'boolean') {
      throw unsupported({
        harnessId,
        message:
          `ACP permission mapping for ${JSON.stringify(permissionMode)} assigns string value ` +
          `${JSON.stringify(target.value)} to boolean session configuration ${JSON.stringify(target.configId)}.`,
      });
    }
    return;
  }
  if (typeof target.value !== 'string') {
    throw unsupported({
      harnessId,
      message:
        `ACP permission mapping for ${JSON.stringify(permissionMode)} assigns boolean value ` +
        `${JSON.stringify(target.value)} to select session configuration ${JSON.stringify(target.configId)}.`,
    });
  }
  const availableValues = configOption.options.flatMap(option =>
    'options' in option
      ? option.options.map(value => value.value)
      : [option.value],
  );
  if (!availableValues.includes(target.value)) {
    throw unsupported({
      harnessId,
      message:
        `ACP permission mapping for ${JSON.stringify(permissionMode)} requires value ` +
        `${JSON.stringify(target.value)} for session configuration ${JSON.stringify(target.configId)}, ` +
        `but the agent advertised ${formatChoices({ values: availableValues })}.`,

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