#17470: feat(cache): per-agent params for cacheRetention control (#17112)

## Summary Fixes #17112. No way to set `cacheRetention` per-agent. Low-traffic agents (e.g., cron jobs running every 30 min) waste money on cache writes ($1.25/MTok) that expire before the next request. ## Root Cause `resolveExtraParams()` only reads from global model defaults (`agents.defaults.models["provider/model"].params`). There is no per-agent override — all agents sharing the same model get identical cache settings. ## Fix Add optional `params` field to `AgentConfig` and resolve it in `resolveExtraParams()`: ```ts // types.agents.ts export type AgentConfig = { // ...existing fields... params?: Record<string, unknown>; }; ``` ```ts // extra-params.ts — resolveExtraParams now accepts agentId const agentConfig = cfg?.agents?.list?.find((a) => a.id === params.agentId); return Object.assign({}, globalParams, agentConfig?.params); ``` Agent params merge on top of global model defaults. Three files changed, no new dependencies. **Config example:** ```json { "agents": { "list": [{ "id": "risk-reviewer", "params": { "cacheRetention": "none" } }] } } ``` ## Test plan - [x] Per-agent params returned when agentId matches - [x] Agent params merge over global model defaults (agent wins) - [x] Unmatched agentId returns undefined (no side effects) ## Local Validation - `pnpm build` ✅ - `pnpm check` (format + tsgo + lint) ✅ - Relevant test suites pass ✅ ## Contribution Checklist - [x] Focused scope — single feature per PR - [x] Clear "what" + "why" in description - [x] AI-assisted (Claude) — reviewed and tested by human - [x] Local validation run (`pnpm build && pnpm check`) *AI-assisted (Claude). Reviewed and tested by human.* <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds per-agent `params` override support to `resolveExtraParams`, allowing individual agents to customize stream parameters (e.g., `cacheRetention`, `temperature`) that previously could only be set globally per model. Agent-level params merge on top of global model defaults, with agent values winning on conflict. - Adds optional `params?: Record<string, unknown>` field to `AgentConfig` type - Extends `resolveExtraParams` and `applyExtraParamsToAgent` with optional `agentId` parameter - Passes `sessionAgentId` through at the call site in `attempt.ts` - Three new tests cover match, merge, and no-match scenarios - Backward-compatible: all new parameters are optional, existing behavior unchanged when `agentId` is not provided <h3>Confidence Score: 5/5</h3> - This PR is safe to merge — it's a small, well-scoped additive feature with proper tests and no breaking changes. - The change is minimal (4 files, ~50 lines of logic), fully backward-compatible (all new parameters are optional), and well-tested. The merge semantics (Object.assign with agent overriding global) are correct and straightforward. The integration point in attempt.ts correctly passes the already-resolved sessionAgentId. No security concerns, no mutation of config objects, and existing call sites don't need updating. - No files require special attention. _{Last reviewed commit: 8c13172} <!-- greptile_other_comments_section --> _{(4/5) You can add custom instructions or style guidelines for the agent [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->