fix(mcp): declare readOnlyHint on find_files/grep/multi_grep (#771)

[gustav-fff]

Closes #771

Root cause

The three #[tool] macros in crates/fff-mcp/src/server.rs:422, :537, and :574 declared no annotations, so tools/list returned annotations: null. Clients that gate read-only access by readOnlyHint (plan mode, read-only sub-agents) treat missing annotations as potentially-mutating and block every fff tool, even though fff only reads the filesystem.

Fix

Add annotations(read_only_hint = true, destructive_hint = false, open_world_hint = false) to each of the three #[tool] attributes (find_files, grep, multi_grep). rmcp's macro emits these into the tools/list response.

Steps to reproduce

Pre-fix, on origin/main:

cargo build -p fff-mcp
cd /tmp && mkdir -p fff-mcp-repro && cd fff-mcp-repro && printf 'hello\n' > a.txt
BIN=/path/to/fff/target/debug/fff-mcp
printf '%s\n' \
'{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"r","version":"0"}}}' \
'{"jsonrpc":"2.0","method":"notifications/initialized"}' \
'{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}' | "$BIN"

Expected: find_files, grep, multi_grep each carry "annotations": {"readOnlyHint": true, "destructiveHint": false}.
Actual (pre-fix): each tool has "annotations": null.

How verified

Rebuilt and re-ran the repro above:

find_files annotations= {"readOnlyHint": true, "destructiveHint": false, "openWorldHint": false}
grep       annotations= {"readOnlyHint": true, "destructiveHint": false, "openWorldHint": false}
multi_grep annotations= {"readOnlyHint": true, "destructiveHint": false, "openWorldHint": false}

cargo build -p fff-mcp clean. Diff is 6 insertions / 3 deletions in one file.

Automated triage via Gustav. Honk-Honk 🪿

Summary by CodeRabbit

• Documentation
  • Clarified descriptions for file-finding and search tools.
  • Added guidance indicating these tools are read-only, non-destructive, and operate within a defined scope.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: d2849888-f3b1-4a7d-ae5f-5a0e47bd5743

📥 Commits

Reviewing files that changed from the base of the PR and between 69651d8 and fbf2398.

📒 Files selected for processing (1)

• crates/fff-mcp/src/server.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• crates/fff-mcp/src/server.rs

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📝 Walkthrough

Walkthrough

The MCP server updates descriptions for find_files, grep, and multi_grep. Each tool now declares read-only, non-destructive, closed-world behavior.

Changes

MCP tool metadata

Layer / File(s)	Summary
Search tool declarations crates/fff-mcp/src/server.rs	The tool descriptions add query guidance, literal-pattern details, examples, and performance notes. The tools also declare read-only, non-destructive, closed-world annotations.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Mergeability Score: ⚪ Minimal · up to fbf23

This localized change only declares accurate read-only metadata for three filesystem-search tools; no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the MCP annotation change for all three affected tools.
Linked Issues check	✅ Passed	The changes satisfy issue #771 by declaring read-only, non-destructive annotations for find_files, grep, and multi_grep.
Out of Scope Changes check	✅ Passed	The changes are limited to tool descriptions and MCP annotations required by issue #771.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch triage-bot/issue-771

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