#22439: feat(workspace): add tiered bootstrap loading with configurable bootstrapTier

Closes #22438 ## Motivation Bootstrap files consume LLM tokens on every session. For users with large workspaces, loading all files into every session — including sub-agents and cron jobs — wastes context window budget on files the agent never references. This PR introduces tiered loading so users can control how much context each session type receives, **reducing unnecessary token usage** while preserving persona consistency where needed. ## What Introduces a three-tier bootstrap file loading system (`minimal` | `standard` | `full`) with a new `agents.defaults.bootstrapTier` configuration option. ## Why The current binary split (main=all, subagent/cron=minimal) doesn't support use cases where subagents need persona context or where main sessions should be lightweight. This adds a clean, backward-compatible middle ground that lets users optimize their token budget per session type. ## How - **`resolveBootstrapTier(sessionKey, tierOverride)`** — Resolves effective tier from session type + optional config override - **`filterBootstrapFilesForSession(files, sessionKey, tierOverride)`** — Extended with optional tier parameter (backward compatible — no tierOverride = existing behavior) - **Config**: `agents.defaults.bootstrapTier` in zod schema, TypeScript types, labels, and help text ## Testing 11 unit tests covering: - Default tier resolution for main/subagent/cron sessions - Config override behavior - File filtering per tier - Backward compatibility (no tier = existing behavior) - Full tier including extra bootstrap files All tests pass. ## Changes | File | Change | |------|--------| | `src/agents/workspace.ts` | `BootstrapTier` type, `resolveBootstrapTier()`, extended filter | | `src/agents/bootstrap-files.ts` | Wire tier from config | | `src/config/zod-schema.agent-defaults.ts` | Zod schema for bootstrapTier | | `src/config/types.agent-defaults.ts` | TypeScript type | | `src/config/schema.labels.ts` | UI label | | `src/config/schema.help.ts` | Help text | | `src/agents/workspace.tiered-bootstrap.test.ts` | 11 tests | 7 files changed, 145 insertions(+), 3 deletions(-)