#22140: feat(config): add usageDefault to agent defaults for persistent /usage mode

## Summary Fixes #22083 Adds `usageDefault` to `AgentDefaultsConfig` so users can persist their preferred `/usage` footer level in `openclaw.json` without re-running `/usage` after every `/new` or restart. ## Usage ```jsonc { "agents": { "defaults": { "usageDefault": "tokens" // off | tokens | full } } } ``` ## Change Type - [x] Feature ## Scope - [x] Config / DX ## Linked Issues Fixes #22083 ## Root Cause `/usage` sets `responseUsage` on the session entry, but this resets on every `/new` or restart. There was no config-level default to fall back to. ## Fix **`src/config/types.agent-defaults.ts`** — added `usageDefault?: "off" | "tokens" | "full"` to `AgentDefaultsConfig`, following the same pattern as `verboseDefault`, `thinkingDefault`, and `elevatedDefault`. **`src/auto-reply/reply/agent-runner.ts`** — extended the `responseUsageRaw` fallback chain: ```ts // Before: const responseUsageRaw = activeSessionEntry?.responseUsage ?? (sessionKey ? activeSessionStore?.[sessionKey]?.responseUsage : undefined); // After: const responseUsageRaw = activeSessionEntry?.responseUsage ?? (sessionKey ? activeSessionStore?.[sessionKey]?.responseUsage : undefined) ?? followupRun.run.config.agents?.defaults?.usageDefault; ``` The `/usage` per-session override continues to work exactly as before — `responseUsage` on the session entry takes precedence over the config default. ## Compatibility / Migration - Backward compatible? Yes — new optional field, defaults to `undefined` (existing behavior unchanged) - Config/env changes? No migration needed; add `usageDefault` to `openclaw.json` to opt in 🤖 AI-Assisted: Yes (via OpenClaw / MIST) <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds `usageDefault` config field to persist `/usage` footer preferences across sessions and restarts, following the same pattern as `verboseDefault`, `thinkingDefault`, and `elevatedDefault`. - Added `usageDefault?: "off" | "tokens" | "full"` to `AgentDefaultsConfig` TypeScript type - Extended fallback chain in `agent-runner.ts` to check config default after session-level overrides - **Critical issue**: Missing Zod schema definition for `usageDefault` field The implementation correctly follows the existing pattern for similar defaults, with proper fallback precedence (session override → config default). However, the Zod schema wasn't updated, which will cause config validation to reject `usageDefault` due to the `.strict()` mode in `AgentDefaultsSchema`. <h3>Confidence Score: 2/5</h3> - Implementation is correct but missing critical schema validation, will break when users try to use the feature - The TypeScript implementation correctly follows existing patterns and the fallback chain is properly ordered. However, the missing Zod schema entry means the feature won't work in practice - config validation will reject `usageDefault` settings, making this a breaking issue that needs to be fixed before merge. - src/config/zod-schema.agent-defaults.ts needs the missing schema field added _{Last reviewed commit: ea26de1} <!-- greptile_other_comments_section --> <!-- /greptile_comment -->