pi-str-replace-editor

Model-facing str_replace_editor (view / create / str_replace / insert) for Pi, enabled only for DeepSeek-family models, where it replaces the built-in read, edit, and write tools.

Why

DeepSeek-family models are tuned on the canonical Claude Code str_replace_editor surface (cat -n views, unique literal old_str, insert-after-line). Serving them pi's edit/write JSON contract wastes tokens and turns. This extension gives DeepSeek models the tool they were trained for and removes the three built-in tools that become redundant (view covers read, create covers write, str_replace/insert cover edit). bash, grep, find, ls stay active.

Semantics are a faithful port of the reference RL harness's str_replace_editor tool; its benchmark suite (tools.spec.ts) is re-characterized in test/engine.test.ts.

Gating

• A model is "deepseek" when its id, provider, or display name matches /deepseek/i (case-insensitive, router-robust).
• session_start + model_select swap the active tool set:
  • deepseek: read/edit/write removed, str_replace_editor added, and grep/find/ls removed by default — leaving bash + str_replace_editor, the harness minimal-preset shape those models were tuned on. Search goes through bash grep -rn/find/ls or str_replace_editor view on a directory.
  • everyone else: str_replace_editor removed, read/edit/write and grep/find/ls restored. GPT-family models keep edit/write exactly as-is (pi-apply-patch owns them there), so the two extensions never fight.
• Defense in depth: tool_call blocks a deepseek model that somehow calls read/edit/write (pointer at str_replace_editor) and any other model that calls str_replace_editor (pointer at read/edit/write). No ordering race between extensions can produce a wrong write.

Config file ~/.pi/agent/pi-str-replace-editor.json (optional):

{
  "mode": "auto",
  "deepseekPatterns": ["deepseek"],
  "extraDisabledTools": ["grep", "find", "ls"]
}

• mode: auto (default) | on (editor for every model) | off.
• deepseekPatterns: regex list tested against id/provider/name.
• extraDisabledTools: additional tool names hidden for deepseek models (default ["grep", "find", "ls"]; set to [] to keep those three).

Improvements over the harness

• Syntax highlighting in the TUI for view results (pi's highlighter), plus a display diff for str_replace results.
• Better errors / fallbacks:
  • old_str not found → closest lines with their line numbers + CRLF hint.
  • relative paths → the cwd-resolved absolute suggestion (Maybe you meant /abs/path?).
  • missing parent directory → mkdir -p hint; vanished files → FS_NOT_FOUND.
  • binary files → refused with a bash/xxd fallback hint.
  • view on an image returns the image as an attachment.
  • prepareArguments accepts legacy shapes (unadvertised): file_path, file:// prefixes, backtick-wrapped paths, replace_all: true.
• Concurrency: every mutation runs inside pi's withFileMutationQueue, so parallel tool calls on the same file serialize instead of losing updates.
• Error codes (FS_NOT_FOUND, FS_EDIT_NOT_FOUND, FS_AMBIGUOUS_EDIT, …) mirror the harness vocabulary.

Development

npm run check:str-replace-editor   # typecheck
npm run test:str-replace-editor    # benchmark port + adversarial battery