aether-agent-core 0.8.7

A minimal Rust library for building AI agents with MCP tool integration
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193

use llm::{LlmCallPurpose, ModelIdentity, SessionUsageEvent, SessionUsageTotals, TokenUsage, UsageCost, UsageSource};

/// Billable usage for one agent session. The root agent's session tracker captures totals for all agents (e.g. sub-agents).
#[derive(Clone, Debug)]
pub struct SessionUsageTracker {
    source: UsageSource,
    sequence: u64,
    totals: SessionUsageTotals,
}

impl SessionUsageTracker {
    pub fn new(agent_name: impl Into<String>) -> Self {
        Self { source: UsageSource::new(agent_name), sequence: 0, totals: SessionUsageTotals::default() }
    }

    /// Continue from the last persisted event so a resumed session keeps its totals.
    pub fn resume_from(&mut self, last: &SessionUsageEvent) {
        self.sequence = last.sequence;
        self.totals = last.totals.clone();
    }

    pub fn source(&self) -> &UsageSource {
        &self.source
    }

    /// Record one of this agent's own calls, priced from the model's catalog entry.
    pub fn record(&mut self, purpose: LlmCallPurpose, model: ModelIdentity, tokens: TokenUsage) -> SessionUsageEvent {
        let estimated_cost = model.pricing.map(|pricing| pricing.estimate_cost(tokens));
        self.push(self.source.clone(), purpose, model, tokens, estimated_cost)
    }

    /// Fold a sub-agent's sample into these totals. The child's model and cost
    /// stand; its lineage is filled in when the child did not know it.
    pub fn record_child(&mut self, task_id: &str, child: SessionUsageEvent) -> SessionUsageEvent {
        let UsageSource { agent_id, parent_agent_id, task_id: child_task_id, agent_name } = child.source;
        let source = UsageSource {
            agent_id,
            parent_agent_id: parent_agent_id.or_else(|| Some(self.source.agent_id.clone())),
            task_id: child_task_id.or_else(|| Some(task_id.to_string())),
            agent_name,
        };
        self.push(source, child.purpose, child.model, child.tokens, child.estimated_cost)
    }

    fn push(
        &mut self,
        source: UsageSource,
        purpose: LlmCallPurpose,
        model: ModelIdentity,
        tokens: TokenUsage,
        estimated_cost: Option<UsageCost>,
    ) -> SessionUsageEvent {
        self.sequence = self.sequence.saturating_add(1);
        self.totals.add(tokens, estimated_cost);
        SessionUsageEvent {
            sequence: self.sequence,
            source,
            purpose,
            model,
            tokens,
            estimated_cost,
            totals: self.totals.clone(),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use llm::testing::{priced_model, session_usage_event};

    #[test]
    fn own_calls_are_sequenced_priced_and_totalled() {
        let mut tracker = SessionUsageTracker::new("root");
        let first = tracker.record(LlmCallPurpose::Chat, ModelIdentity::default(), TokenUsage::new(2, 3));
        let second =
            tracker.record(LlmCallPurpose::Chat, ModelIdentity::of(Some(&priced_model())), TokenUsage::new(5, 7));

        assert_eq!((first.sequence, second.sequence), (1, 2));
        assert_eq!(first.source, *tracker.source());
        assert!(first.estimated_cost.is_none());
        assert!(second.estimated_cost.is_some());
        assert_eq!(second.totals.tokens.input_tokens.get(), 7);
        assert_eq!(second.totals.tokens.output_tokens.get(), 10);
        assert_eq!(second.totals.unpriced_calls, 1);
        assert!(second.totals.estimated_usd.get() > 0.0);
    }

    #[test]
    fn zero_token_samples_without_pricing_stay_fully_priced() {
        let mut tracker = SessionUsageTracker::new("root");
        let event = tracker.record(LlmCallPurpose::Chat, ModelIdentity::default(), TokenUsage::default());
        assert!(event.totals.is_fully_priced());
    }

    #[test]
    fn resumed_tracker_continues_sequence_and_totals() {
        let mut tracker = SessionUsageTracker::new("root");
        let last = tracker.record(LlmCallPurpose::Chat, ModelIdentity::default(), TokenUsage::new(4, 6));

        let mut resumed = SessionUsageTracker::new("root");
        resumed.resume_from(&last);
        let next = resumed.record(LlmCallPurpose::Compaction, ModelIdentity::default(), TokenUsage::new(1, 1));
        assert_eq!(next.sequence, 2);
        assert_eq!(next.totals.tokens.input_tokens.get(), 5);
        assert_eq!(next.totals.tokens.output_tokens.get(), 7);
        assert_eq!(next.totals.unpriced_calls, 2);
    }

    #[test]
    fn child_samples_are_resequenced_totalled_and_given_lineage() {
        let mut tracker = SessionUsageTracker::new("root");
        let mut child = session_usage_event(9, TokenUsage::new(8, 4));
        child.source = UsageSource::new("explorer");

        let folded = tracker.record_child("task_0", child.clone());
        let own = tracker.record(LlmCallPurpose::Chat, ModelIdentity::default(), TokenUsage::new(1, 1));

        assert_eq!(folded.sequence, 1);
        assert_eq!(folded.source.agent_id, child.source.agent_id);
        assert_eq!(folded.source.agent_name, "explorer");
        assert_eq!(folded.source.parent_agent_id.as_deref(), Some(tracker.source().agent_id.as_str()));
        assert_eq!(folded.source.task_id.as_deref(), Some("task_0"));
        assert_eq!(folded.tokens, child.tokens);
        assert_eq!(own.sequence, 2);
        assert_eq!(own.totals.tokens.input_tokens.get(), 9);
        assert_eq!(own.totals.unpriced_calls, 2);
    }

    #[test]
    fn nested_samples_and_resumption_preserve_cumulative_cost_components() {
        let model = ModelIdentity::of(Some(&priced_model()));
        let tokens = TokenUsage {
            cache_read_tokens: Some(20.into()),
            cache_creation_tokens: Some(10.into()),
            ..TokenUsage::new(100, 50)
        };

        let mut root = SessionUsageTracker::new("root");
        root.record(LlmCallPurpose::Chat, model.clone(), tokens);

        let mut child = SessionUsageTracker::new("child");
        let child_sample = child.record(LlmCallPurpose::Chat, model.clone(), tokens);
        root.record_child("child-task", child_sample);

        let mut grandchild = SessionUsageTracker::new("grandchild");
        let sample = grandchild.record(LlmCallPurpose::Compaction, model.clone(), tokens);
        let sample_cost = sample.estimated_cost.unwrap();
        let folded = child.record_child("grandchild-task", sample);

        let last = root.record_child("child-task", folded);

        assert_eq!(last.sequence, 3);
        assert_eq!(last.source.agent_id, grandchild.source().agent_id);
        assert_eq!(last.totals.tokens.input_tokens.get(), 300);
        assert_eq!(last.estimated_cost, Some(sample_cost));
        assert_cost_components(&last, sample_cost, 3);

        let persisted = serde_json::to_string(&last).unwrap();
        let mut resumed = SessionUsageTracker::new("root");
        resumed.resume_from(&serde_json::from_str(&persisted).unwrap());
        let next = resumed.record(LlmCallPurpose::Chat, model, tokens);
        assert_eq!(next.sequence, 4);
        assert_eq!(next.totals.tokens.input_tokens.get(), 400);
        assert_cost_components(&next, sample_cost, 4);
    }

    fn assert_cost_components(event: &SessionUsageEvent, cost: UsageCost, samples: usize) {
        let totals = serde_json::to_value(&event.totals).unwrap();
        for (field, amount) in [
            ("estimated_input_usd", cost.input_usd),
            ("estimated_output_usd", cost.output_usd),
            ("estimated_cache_read_usd", cost.cache_read_usd),
            ("estimated_cache_creation_usd", cost.cache_creation_usd),
            ("estimated_usd", cost.total_usd),
        ] {
            let expected = (0..samples).fold(llm::Usd::ZERO, |total, _| total + amount);
            assert_eq!(totals[field], serde_json::json!(expected), "{field}");
        }
    }

    #[test]
    fn child_samples_keep_lineage_they_already_carry() {
        let mut tracker = SessionUsageTracker::new("root");
        let mut grandchild = session_usage_event(1, TokenUsage::new(1, 1));
        grandchild.source.parent_agent_id = Some("middle".to_string());
        grandchild.source.task_id = Some("task_7".to_string());

        let folded = tracker.record_child("task_0", grandchild);
        assert_eq!(folded.source.parent_agent_id.as_deref(), Some("middle"));
        assert_eq!(folded.source.task_id.as_deref(), Some("task_7"));
    }
}