[codex] feat(cli): add built-in subagents

[yzlu0917]

Summary

• add built-in CLI subagents that are available without extra config.yaml setup
• fall back to built-in planner, researcher, and reviewer subagents when no explicit subagent models are configured
• keep configured subagent models taking precedence over the built-in defaults
• cover the fallback and precedence behavior with ModelService regression tests

Why

The beta subagent tool already exists in the CLI, but trying it currently requires internal-only subagent model configuration. This change makes the feature usable out of the box by cloning the current chat model into a few specialized built-in subagents with hard-coded prompts in extensions/cli.

Validation

• ran npm test -- src/services/ModelService.test.ts src/tools/subagent.test.ts
• ran npm run lint in extensions/cli (passes with two existing repo warnings in unrelated files)

Closes #9550

---

Summary by cubic

Adds built-in CLI subagents (planner, researcher, reviewer) so the beta Subagent tool works out of the box and still honors explicitly configured subagent models (closes #9550). Each built-in clones the current chat model with a specialized prompt.

• New Features

  • Added built-in agent definitions and prompts; CLI help text mentions them.
  • ModelService.getSubagentModels prefers configured subagents; otherwise falls back to built-ins cloned from the active chat model.
  • Tests cover precedence, fallback, and the no-base-model case.

• Bug Fixes

  • Hardened subagent lookup and preview to handle missing model names.

^{Written for commit 4ec8449. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 7 files

[chatgpt-codex-connector]

💡 Codex Review

continue/core/util/history.ts

Line 42 in 4ec8449

if (options.workspaceDirectory) {

Apply workspace filter even for empty workspace keys

The new workspace filter is guarded by a truthy check, so passing workspaceDirectory: "" (the value used for sessions created without a workspace) skips filtering and returns all sessions instead of only no-workspace sessions. This makes history scoping incorrect in no-folder contexts and can surface unrelated project sessions when callers pass the current workspace value directly. Check for undefined/null rather than truthiness before filtering.

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