lean_ctx/tools/registered/
ctx_delta.rs

1use rmcp::ErrorData;
2use rmcp::model::Tool;
3use serde_json::{Map, Value, json};
4
5use crate::server::tool_trait::{McpTool, ToolContext, ToolOutput, require_resolved_path};
6use crate::tool_defs::tool_def;
7
8pub struct CtxDeltaTool;
9
10impl McpTool for CtxDeltaTool {
11    fn name(&self) -> &'static str {
12        "ctx_delta"
13    }
14
15    fn tool_def(&self) -> Tool {
16        tool_def(
17            "ctx_delta",
18            "Incremental diff since last read — shows only changed lines after you edit.\n\
19             WORKFLOW: ctx_read(mode=full) -> edit -> ctx_delta (no re-read needed).\n\
20             Use INSTEAD of re-reading the whole file after modifications — saves 90%+ tokens\n\
21             on unchanged content. Path must have a prior ctx_read in this session\'s cache.\n\
22             For the full git diff against HEAD, use ctx_read(path, mode=diff) instead.",
23            json!({
24                "type": "object",
25                "properties": {
26                    "path": { "type": "string", "description": "File path" }
27                },
28                "required": ["path"]
29            }),
30        )
31    }
32
33    fn handle(
34        &self,
35        args: &Map<String, Value>,
36        ctx: &ToolContext,
37    ) -> Result<ToolOutput, ErrorData> {
38        let path = require_resolved_path(ctx, args, "path")?;
39
40        {
41            let cache_lock = ctx
42                .cache
43                .as_ref()
44                .ok_or_else(|| ErrorData::internal_error("cache not available", None))?;
45            let Some(mut cache) =
46                crate::server::bounded_lock::write(cache_lock, "ctx_delta cache write")
47            else {
48                crate::core::io_health::record_freeze();
49                return Err(ErrorData::internal_error(
50                    "cache busy (ctx_delta) — retry in a moment",
51                    None,
52                ));
53            };
54            let output = crate::tools::ctx_delta::handle(&mut cache, &path);
55            let original = cache.get(&path).map_or(0, |e| e.original_tokens);
56            let tokens = crate::core::tokens::count_tokens(&output);
57            drop(cache);
58
59            if let Some(session_lock) = ctx.session.as_ref() {
60                let mut session = session_lock.blocking_write();
61                session.mark_modified(&path);
62            }
63
64            let saved = original.saturating_sub(tokens);
65            Ok(ToolOutput {
66                text: output,
67                original_tokens: original,
68                saved_tokens: saved,
69                mode: Some("delta".to_string()),
70                path: Some(path),
71                changed: false,
72                shell_outcome: None,
73                content_blocks: None,
74            })
75        }
76    }
77}
lean_ctx/tools/registered/ctx_delta.rs

lean_ctx/tools/registered/
ctx_delta.rs
