refactor(agent-presets): keep the user-root segment out of the package API

`USER_PRESET_DIR` was exported with no production consumer — only the new test
read it, and a test that imports the implementation constant cannot catch that
constant being wrong. It stays module-internal, and the test spells the segment
it expects.

packages/preset/agent-presets/src/discovery.ts

@@ -33,6 +33,10 @@ export const COMPOSITION_FILE = 'agent.cordis.yml'
  * the installed app can resolve; where a person's own presets go is the same
  * place in every deployment that does not say otherwise, so a launcher that
  * forgets to configure one still finds them.
+ *
+ * Package-internal on purpose: no consumer outside this package addresses the
+ * directory by name, and a test that imported it could not catch this value
+ * being wrong — the expected segment is spelled out where it is asserted.
  */
 export const USER_PRESET_DIR = '.agent-presets'
 

packages/preset/agent-presets/src/index.ts

@@ -50,7 +50,7 @@ export const AgentPresetSettingsSchema: z<AgentPresetSettings> = z.object({
   default: z.string(),
 })
 
-export { COMPOSITION_FILE, discoverPresets, scanRoot, USER_PRESET_DIR } from './discovery.ts'
+export { COMPOSITION_FILE, discoverPresets, scanRoot } from './discovery.ts'
 export {
   METADATA_FILE, readPresetMetadata, renderPresetMetadata, type PresetMetadata,
 } from './metadata.ts'