Method is_overflow

crates/opencode-session/src/compaction.rs:203–230

Check whether the conversation has overflowed the context window. Mirrors TS `isOverflow`. The `total` field on `TokenUsage` is used first; if it is zero we fall back to summing the individual fields (input + output + cache_read + cache_write) -- matching the TS `input.tokens.total || input.tokens.input + ...` logic.

(&self, usage: &TokenUsage, limits: &ModelLimits)

    /// (input + output + cache_read + cache_write) -- matching the TS
    /// `input.tokens.total || input.tokens.input + ...` logic.
    pub fn is_overflow(&self, usage: &TokenUsage, limits: &ModelLimits) -> bool {
        if !self.config.auto {
            return false;
        }

        if limits.context == 0 {
            return false;
        }

        // TS: const count = input.tokens.total || input.tokens.input + ...
        let count = if usage.total > 0 {
            usage.total
        } else {
            usage.input + usage.output + usage.cache_read + usage.cache_write
        };

        let reserved = self
            .config
            .reserved
            .unwrap_or_else(|| COMPACTION_BUFFER.min(limits.max_output));

        let usable = limits
            .max_input
            .map(|input| input.saturating_sub(reserved))
            .unwrap_or_else(|| limits.context.saturating_sub(limits.max_output));

        count >= usable
    }

    pub fn estimate_tokens(text: &str) -> u64 {
        let char_count = text.chars().count() as u64;