1. 1//! How much of one tool result a request carries
2. 2//! (docs/design/68-context-engine.md §3).
3. 3//!
4. 4//! A tool returns its whole result and the agent loop records it whole in the
5. 5//! ledger; a request carries a result verbatim up to [`RESULT_WINDOW_CHARS`].
6. 6//! Past that, the request carries a *window*: whole lines from the start and
7. 7//! the end, and one line in place of the rest that says exactly which lines
8. 8//! were left out, how many characters they hold, and the `recall` call that
9. 9//! returns them. Inside a window, a line longer than [`LINE_WINDOW_CHARS`]
10. 10//! shows its start and says how many characters it continues for. Nothing is
11. 11//! left out without the request saying so, and nothing is lost from the
12. 12//! ledger.
13. 13
14. 14/// Most characters of one result a request carries verbatim.
15. 15pub const RESULT_WINDOW_CHARS: usize = 30_000;
16. 16/// Most characters of one line a window shows. A result that fits whole is
17. 17/// never windowed, however long its lines.
18. 18pub const LINE_WINDOW_CHARS: usize = 2_000;
19. 19
20. 20/// The window a request carries for `content`, or `None` when it fits whole.
21. 21///
22. 22/// `recall_id` is the evidence id the omitted lines can be recalled by (the
23. 23/// call's `tool_use_id`); without one the note only states what was left out.
24. 24/// `first_line` is the 1-based number of `content`'s first line within that
25. 25/// evidence, so a window over a recalled range names the evidence's own line
26. 26/// numbers.
27. 27pub fn window(content: &str, recall_id: Option<&str>, first_line: usize) -> Option<String> {
28. 28 if content.chars().count() <= RESULT_WINDOW_CHARS {
29. 29 return None;
30. 30 }
31. 31 let lines: Vec<&str> = content.lines().collect();
32. 32 let first_line = first_line.max(1);
33. 33 let shown: Vec<String> = lines
34. 34 .iter()
35. 35 .map(|line| {
36. 36 let chars = line.chars().count();
37. 37 if chars <= LINE_WINDOW_CHARS {
38. 38 (*line).to_string()
39. 39 } else {
40. 40 let kept: String = line.chars().take(LINE_WINDOW_CHARS).collect();
41. 41 format!(
42. 42 "{kept} [line continues for {} more chars]",
43. 43 chars - LINE_WINDOW_CHARS
44. 44 )
45. 45 }
46. 46 })
47. 47 .collect();
48. 48 let cost = |line: &String| line.chars().count() + 1;
49. 49
50. 50 let head_budget = RESULT_WINDOW_CHARS * 2 / 5;
51. 51 let tail_budget = RESULT_WINDOW_CHARS - head_budget;
52. 52 let mut head_end = 0;
53. 53 let mut used = 0;
54. 54 while head_end < shown.len() && used + cost(&shown[head_end]) <= head_budget {
55. 55 used += cost(&shown[head_end]);
56. 56 head_end += 1;
57. 57 }
58. 58 let mut tail_start = shown.len();
59. 59 used = 0;
60. 60 while tail_start > head_end && used + cost(&shown[tail_start - 1]) <= tail_budget {
61. 61 used += cost(&shown[tail_start - 1]);
62. 62 tail_start -= 1;
63. 63 }
64. 64
65. 65 let mut out: Vec<String> = shown[..head_end].to_vec();
66. 66 if head_end < tail_start {
67. 67 let omitted_chars: usize = lines[head_end..tail_start]
68. 68 .iter()
69. 69 .map(|line| line.chars().count() + 1)
70. 70 .sum();
71. 71 let start = first_line + head_end;
72. 72 let end = first_line + tail_start - 1;
73. 73 let span = if start == end {
74. 74 format!("line {start}")
75. 75 } else {
76. 76 format!("lines {start}\u{2013}{end}")
77. 77 };
78. 78 let note = match recall_id {
79. 79 Some(id) => format!(
80. 80 "[{span} omitted ({omitted_chars} chars); recall {{\"id\": \"{id}\", \"range\": {{\"start\": {start}, \"end\": {end}}}}} returns them]"
81. 81 ),
82. 82 None => format!("[{span} omitted ({omitted_chars} chars)]"),
83. 83 };
84. 84 out.push(note);
85. 85 }
86. 86 out.extend(shown[tail_start..].iter().cloned());
87. 87 Some(out.join("\n"))
88. 88}
89. 89
90. 90/// `content` as a caller with no ledger to keep the whole in passes it on
91. 91/// (a flow node's output, a scheduled script's report): whole, or its window
92. 92/// when over-long.
93. 93pub fn bounded(content: String) -> String {
94. 94 window(&content, None, 1).unwrap_or(content)
95. 95}
96. 96
97. 97#[cfg(test)]
98. 98#[allow(clippy::unwrap_used, clippy::expect_used)]
99. 99mod tests {
100. 100 use super::*;
101. 101
102. 102 #[test]
103. 103 fn a_result_that_fits_is_not_windowed() {
104. 104 assert_eq!(window("one\ntwo", Some("call-1"), 1), None);
105. 105 }
106. 106
107. 107 #[test]
108. 108 fn an_over_long_result_keeps_whole_lines_and_names_what_it_left_out() {
109. 109 let content: String = (1..=5000)
110. 110 .map(|n| format!("line number {n:05}\n"))
111. 111 .collect();
112. 112 let windowed = window(&content, Some("call-7"), 1).expect("windowed");
113. 113 assert!(windowed.chars().count() <= RESULT_WINDOW_CHARS + 200);
114. 114 assert!(windowed.starts_with("line number 00001\n"));
115. 115 assert!(windowed.ends_with("line number 05000"));
116. 116 let note = windowed
117. 117 .lines()
118. 118 .find(|line| line.starts_with("[lines "))
119. 119 .expect("omission note");
120. 120 assert!(note.contains("recall {\"id\": \"call-7\""), "{note}");
121. 121 for line in windowed.lines().filter(|line| !line.starts_with('[')) {
122. 122 assert!(line.starts_with("line number "), "cut line: {line}");
123. 123 assert_eq!(line.len(), "line number 00000".len());
124. 124 }
125. 125 }
126. 126
127. 127 #[test]
128. 128 fn the_omitted_range_is_numbered_within_the_evidence() {
129. 129 let content: String = (1..=5000).map(|n| format!("row {n:05}\n")).collect();
130. 130 let windowed = window(&content, Some("call-2"), 101).expect("windowed");
131. 131 let note = windowed
132. 132 .lines()
133. 133 .find(|line| line.starts_with("[lines "))
134. 134 .expect("omission note");
135. 135 let shown_head = windowed
136. 136 .lines()
137. 137 .take_while(|line| !line.starts_with('['))
138. 138 .count();
139. 139 assert!(
140. 140 note.starts_with(&format!("[lines {}\u{2013}", 101 + shown_head)),
141. 141 "{note}"
142. 142 );
143. 143 }
144. 144
145. 145 #[test]
146. 146 fn a_long_line_that_fits_is_carried_whole() {
147. 147 let long = "x".repeat(LINE_WINDOW_CHARS * 5);
148. 148 assert_eq!(window(&long, Some("call-3"), 1), None);
149. 149 }
150. 150
151. 151 #[test]
152. 152 fn inside_a_window_a_long_line_says_how_much_it_continues_for() {
153. 153 let long = "x".repeat(RESULT_WINDOW_CHARS);
154. 154 let windowed = window(&format!("head\n{long}\ntail"), None, 1).expect("windowed");
155. 155 let continues = RESULT_WINDOW_CHARS - LINE_WINDOW_CHARS;
156. 156 assert!(windowed.contains(&format!("[line continues for {continues} more chars]")));
157. 157 assert!(windowed.starts_with("head\n") && windowed.ends_with("\ntail"));
158. 158 }
159. 159
160. 160 #[test]
161. 161 fn multibyte_content_is_counted_in_chars() {
162. 162 let content = "é".repeat(RESULT_WINDOW_CHARS);
163. 163 let lines: String = content
164. 164 .chars()
165. 165 .collect::<Vec<_>>()
166. 166 .chunks(100)
167. 167 .map(|chunk| chunk.iter().collect::<String>() + "\n")
168. 168 .collect();
169. 169 let windowed = window(&lines, None, 1).expect("windowed");
170. 170 assert!(windowed.chars().count() <= RESULT_WINDOW_CHARS + 200);
171. 171 }
172. 172}
173. 173