New (experimental) edit tool

[lyssieth]

Adds a new edit tool that improves upon str-replace, and should generally be more reliable and easier to reach for.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 1ab1cd3a-018b-44fe-92ff-98aca3c9c961

📥 Commits

Reviewing files that changed from the base of the PR and between 0036012 and a0f81bd.

📒 Files selected for processing (6)

• config/agent/tools.toml.example
• packages/runtime/src/engine/prune.ts
• packages/runtime/src/engine/tools.ts
• packages/runtime/src/engine/tools/edit.test.ts
• packages/runtime/src/engine/tools/edit.ts
• packages/runtime/src/engine/tools/index.ts

---

📝 Walkthrough

Walkthrough

This PR adds a new edit tool for fuzzy string replacement in files. The implementation includes whitespace-tolerant matching, optional near-anchor scoping, frontmatter preservation, and detailed error reporting. The tool is integrated into the runtime registry, build system, and token budget management, with comprehensive test coverage.

Changes

Edit Tool Feature

Layer / File(s)	Summary
Edit tool schema, matching, and execution packages/runtime/src/engine/tools/edit.ts	Defines input schema for path, old_text, new_text, optional near anchor, and all-flag. Implements fuzzy-matching utilities for whitespace-insensitive normalization and character-by-character comparison. Adds context formatting for error messages. Implements execute flow: resolves and permission-checks the path, reads file content, preserves frontmatter when required, finds fuzzy matches (optionally scoped by near anchors), validates match counts, applies replacements with offset tracking, writes updated content, invalidates session cache, and returns success with context and replaced count.
Tool registry and import packages/runtime/src/engine/tools/index.ts	Imports the edit tool module and registers it in builtinToolRegistry to make it available as a built-in tool.
Build system tool enablement and deprecation packages/runtime/src/engine/tools.ts	Precomputes an enabledTools set from configuration and derives an editEnabled flag. When edit is enabled, marks str-replace with a deprecated label and updates the write tool description to reference edit instead of str-replace.
Token budget eviction packages/runtime/src/engine/prune.ts	Adds "edit" to the evictable tool-response names so edit tool responses can be superseded when the token budget is exceeded.
Configuration example config/agent/tools.toml.example	Enables the edit tool by default in the example configuration file.
Edit tool test suite packages/runtime/src/engine/tools/edit.test.ts	Comprehensive Vitest suite validating exact and fuzzy text matching, whitespace normalization, all flag semantics, near-scoped anchoring with ±15-line windows, frontmatter preservation for block and skill formats, error messages with file excerpts, and empty old_text rejection. Includes filesystem mocking and ToolContext scaffolding.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: introducing a new experimental edit tool, which aligns with the changeset's core objective.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}