#23562: feat: add sessionFreshness config for isolated cron jobs (#23539)

## Summary - Adds a `sessionFreshness` field to `CronJob` (`"reuse-if-fresh"` | `"always-new"`) - When set to `"always-new"`, each isolated cron run gets a brand-new session UUID, preventing context accumulation across runs - Default (`undefined` / `"reuse-if-fresh"`) preserves existing behavior ## Problem PR #18031 changed isolated cron jobs to reuse session IDs when fresh, contradicting the documented guarantee that "each run starts a fresh session." This caused stale data references and 20–50% token overhead from accumulated context. ## Changes - `src/cron/types.ts` — new `CronSessionFreshness` type and optional field on `CronJob` - `src/cron/normalize.ts` — normalization + validation (case-insensitive) - `src/cron/isolated-agent/run.ts` — wires `sessionFreshness === "always-new"` to existing `forceNew` param in `resolveCronSession()` - `src/cron/service/jobs.ts` — passes through field in `createJob()` and `applyJobPatch()` - `src/cron/normalize.test.ts` — 3 new tests ## Usage \`\`\`json { "sessionFreshness": "always-new", "sessionTarget": "isolated" } \`\`\` Closes #23539 <!-- greptile_comment --> <h3>Greptile Summary</h3> Adds an optional `sessionFreshness` configuration field to control session reuse behavior for isolated cron jobs. When set to `"always-new"`, each cron run creates a fresh session UUID, preventing context accumulation. The default behavior (`undefined` or `"reuse-if-fresh"`) preserves the existing session reuse logic introduced in PR #18031. The implementation: - Defines a new `CronSessionFreshness` type with two valid values: `"reuse-if-fresh"` and `"always-new"` - Adds normalization logic with case-insensitive string handling and validation - Wires the field through the job creation and update pipelines (`createJob`, `applyJobPatch`) - Passes `forceNew: true` to `resolveCronSession()` when `sessionFreshness === "always-new"` - Includes comprehensive test coverage for normalization of valid and invalid values <h3>Confidence Score: 5/5</h3> - This PR is safe to merge with minimal risk - The implementation is clean, well-tested, and follows existing patterns in the codebase. It introduces a backward-compatible optional field with proper validation, normalization, and test coverage. The change is minimal and focused, touching only the necessary files to wire through the new configuration option. - No files require special attention _{Last reviewed commit: 3ed4954} <!-- 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 -->