move context functions from agent/context.rs to thought/context.rs

trim_conversation moved to thought/context.rs where model_context_window,
msg_token_count, is_context_overflow, is_stream_error already lived.
Delete the duplicate agent/context.rs (94 lines).

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/agent/context.rs

@@ -1,94 +0,0 @@
-// context.rs — Context window management
-//
-// Token counting and conversation trimming for the context window.
-
-use crate::agent::types::*;
-use tiktoken_rs::CoreBPE;
-
-/// Look up a model's context window size in tokens.
-pub fn model_context_window(_model: &str) -> usize {
-    crate::config::get().api_context_window
-}
-
-/// Context budget in tokens: 60% of the model's context window.
-fn context_budget_tokens(model: &str) -> usize {
-    model_context_window(model) * 60 / 100
-}
-
-/// Trim conversation to fit within the context budget.
-/// Returns the trimmed conversation messages (oldest dropped first).
-pub fn trim_conversation(
-    context: &ContextState,
-    conversation: &[Message],
-    model: &str,
-    tokenizer: &CoreBPE,
-) -> Vec<Message> {
-    let count = |s: &str| tokenizer.encode_with_special_tokens(s).len();
-    let max_tokens = context_budget_tokens(model);
-
-    let identity_cost = count(&context.system_prompt)
-        + context.personality.iter().map(|(_, c)| count(c)).sum::<usize>();
-    let journal_cost: usize = context.journal.iter().map(|e| count(&e.content)).sum();
-    let reserve = max_tokens / 4;
-    let available = max_tokens
-        .saturating_sub(identity_cost)
-        .saturating_sub(journal_cost)
-        .saturating_sub(reserve);
-
-    let msg_costs: Vec<usize> = conversation.iter()
-        .map(|m| msg_token_count(tokenizer, m)).collect();
-    let total: usize = msg_costs.iter().sum();
-
-    let mut skip = 0;
-    let mut trimmed = total;
-    while trimmed > available && skip < conversation.len() {
-        trimmed -= msg_costs[skip];
-        skip += 1;
-    }
-
-    // Walk forward to user message boundary
-    while skip < conversation.len() && conversation[skip].role != Role::User {
-        skip += 1;
-    }
-
-    conversation[skip..].to_vec()
-}
-
-/// Count the token footprint of a message using BPE tokenization.
-pub fn msg_token_count(tokenizer: &CoreBPE, msg: &Message) -> usize {
-    let content = msg.content.as_ref().map_or(0, |c| match c {
-        MessageContent::Text(s) => tokenizer.encode_with_special_tokens(s).len(),
-        MessageContent::Parts(parts) => parts.iter()
-            .map(|p| match p {
-                ContentPart::Text { text } => tokenizer.encode_with_special_tokens(text).len(),
-                ContentPart::ImageUrl { .. } => 85,
-            })
-            .sum(),
-    });
-    let tools = msg.tool_calls.as_ref().map_or(0, |calls| {
-        calls.iter()
-            .map(|c| tokenizer.encode_with_special_tokens(&c.function.arguments).len()
-                    + tokenizer.encode_with_special_tokens(&c.function.name).len())
-            .sum()
-    });
-    content + tools
-}
-
-/// Detect context window overflow errors from the API.
-pub fn is_context_overflow(err: &anyhow::Error) -> bool {
-    let msg = err.to_string().to_lowercase();
-    msg.contains("context length")
-        || msg.contains("token limit")
-        || msg.contains("too many tokens")
-        || msg.contains("maximum context")
-        || msg.contains("prompt is too long")
-        || msg.contains("request too large")
-        || msg.contains("input validation error")
-        || msg.contains("content length limit")
-        || (msg.contains("400") && msg.contains("tokens"))
-}
-
-/// Detect model/provider errors delivered inside the SSE stream.
-pub fn is_stream_error(err: &anyhow::Error) -> bool {
-    err.to_string().contains("model stream error")
-}