hmbown--codewhale/docs/RUNTIME_SIMPLIFICATION_DESIGN.md

Codewhale Runtime Simplification Design

Status: Pre-implementation design record for the v0.9.1 cutover, kept for its "Rejected alternatives" provenance. It is not current runtime documentation and it shipped differently in two ways:

• Goal 3 below ("keeping every legacy tool name registered but hidden") was reversed. The per-action file/git/run/web and exec_shell* names were removed, not hidden — crates/tui/src/tools/registry.rs:2066-2088 and :2290-2304 assert they must stay unregistered. Only apply_patch and the task_* / github_* / automation_* / rlm_* / checklist_* families survive as hidden aliases.
• The default-active policy is nine names, not ten. update_plan and Web are not in DEFAULT_ACTIVE_NATIVE_TOOLS (crates/tui/src/core/engine/tool_catalog.rs:44-58).

For the current contract see TOOL_SURFACE.md.

Goal

Make the model-facing runtime smaller, calmer, and easier for models to use by:

1. Collapsing the long tail of single-purpose file, git, run, and web tools into a few canonical action-based tools.
2. Shrinking the system prompt to durable behavioral invariants and per-turn permission deltas.
3. Keeping every legacy tool name registered but hidden so old transcripts, saved sessions, and recorded automation replay without migration.

Target model-facing surface (default active)

Tool	Actions / Niche
Bash	run, wait, interact, cancel (existing)
File	read, list, search_name, search_content, write, edit, patch
Git	status, diff, log, show, blame
Run	tests, verifiers
Web	search, fetch, wait (deferred unless network is enabled; hidden aliases for legacy names)
tasks	durable task family (existing action-based surface)
github	durable GitHub family (existing; deferred by default)
automation	durable automation family (existing; deferred by default)
rlm	durable RLM family (existing; deferred by default)
agent	sub-agent dispatch
remember	opt-in durable user-memory capture; eager whenever registered
todo_write	progress / plan-of-work updates
update_plan	plan artifact updates
tool_search	on-demand discovery of deferred tools

Default-active policy: 10 names (vs. ~18 before the simplification), with remember registered only for built-in-memory users and the durable families and Web discoverable via tool_search when needed. tool_search itself is a synthetic always-active catalog entry.

Rejected alternatives

• Keep every tool but defer the rare ones. This only changes what is advertised, not how many distinct schemas the model must learn. It also leaves duplicated guidance in the prompt.
• Route search and git through Bash. grep_files, file_search, and the git tools return structured, workspace-aware output and respect sandbox, .gitignore, and network policy. Shell would force the model to re-parse free-form text and lose those guarantees, so dedicated tools win.
• One mega File tool plus a separate Edit tool. A single File tool is only slightly larger than a read/edit pair and keeps the boundary the model already understands (read is cheap, edit requires prior read). Splitting would re-introduce a two-tool alias for the same underlying operations.
• Delete legacy tools. Saved transcripts and replay tests rely on the old names. Removing them would require a config migration and break reproducibility. Hidden aliases avoid both.

Compatibility

• Legacy names (read_file, write_file, edit_file, list_dir, file_search, grep_files, apply_patch, git_status, git_diff, git_log, git_show, git_blame, run_tests, run_verifiers, web_search, fetch_url, wait_for_dev_server) stay registered with model_visible = false.
• The engine resolves calls by name, so old transcripts replay without changes.
• DEFAULT_ACTIVE_NATIVE_TOOLS is updated to list the new canonical names only; hidden legacy tools are ignored by catalog construction.

Prompt simplification

• Replace the tool-calling recipe sections in AGENT_MODE and SUBAGENT_OUTPUT_FORMAT with short references to the canonical tools.
• Reduce mode deltas to permission statements (Act = write requires approval, Plan = no writes or shell, Full Access = auto-approved, Operate = coordinate from ordinary messages).
• Keep the BASE_PROMPT behavioral invariants, LANGUAGE_PROMPT, and OUTPUT_PROMPT intact.
• Move detailed templates (COMPACT_TEMPLATE, sub-agent brief format, planning artifact template) out of the stable prefix and into tool schemas or conditional blocks.

Validation

• Provider-free: scripts/measure-runtime-contract.py reports active tool count and prompt bytes before and after.
• Behavior-preserving: targeted unit tests for File, Git, Run, and Web dispatch against legacy inputs.
• Regression: cargo fmt, cargo clippy --workspace --all-targets --locked, cargo test -p codewhale-tui --bin codewhale-tui --locked, and cargo test --workspace.

v0.9.1 receipt

The source contract and provider-free metric now exercise the complete policy, including opt-in remember:

Contract	Before	After
Default active tools	18	10
Agent-mode instruction bytes	4,064	663
Full system-prompt bytes	15,842	15,368

The final active names are Bash, File, Git, Run, agent, remember, tasks, update_plan, todo_write, and tool_search. remember is present only when built-in memory is enabled; it is eager whenever registered. File advertises only read actions in Plan mode, and its patch action appears only when the existing apply-patch feature is enabled. Hidden aliases remain executable for transcript replay but are absent from the model catalog.