refactor: extract context window token status (#29664)

## Why This PR keeps the mechanical helper extraction separate from the behavior change in #29665. The follow-up needs the token-window accounting from `turn.rs` in another call path, but reviewing that is much easier when the helper extraction is separate from the semantic change. ## What - Adds `session/context_window.rs` with `ContextWindowTokenStatus`. - Moves the existing auto-compaction token-status calculation out of `session/turn.rs`. - Replaces the duplicated inline remaining-token calculation in `turn.rs` with `tokens_until_compaction()`. This PR is intended to be behavior-preserving. The `get_context_remaining` behavior change is stacked separately in #29665. ## Testing - `just test -p codex-core auto_compact_body_after_prefix` --- [//]: # (BEGIN SAPLING FOOTER) Stack created with [Sapling](https://sapling-scm.com). Best reviewed with [ReviewStack](https://reviewstack.dev/openai/codex/pull/29664). * #29665 * __->__ #29664
2026-07-01 00:31:56 +08:00 · 2026-06-23 15:49:30 -07:00
parent 829f5b6b59
commit 4dde907d27
3 changed files with 86 additions and 76 deletions
@@ -0,0 +1,76 @@
+use super::session::Session;
+use super::turn_context::TurnContext;
+use codex_protocol::config_types::AutoCompactTokenLimitScope;
+
+#[derive(Debug)]
+pub(crate) struct ContextWindowTokenStatus {
+    // Full active context usage, independent of the configured auto-compact scope.
+    pub(crate) active_context_tokens: i64,
+    // Usage counted against `model_auto_compact_token_limit` for the current scope.
+    pub(crate) auto_compact_scope_tokens: i64,
+    pub(crate) auto_compact_scope_limit: i64,
+    pub(crate) full_context_window_limit: Option<i64>,
+    pub(crate) auto_compact_window_prefill_tokens: Option<i64>,
+    pub(crate) full_context_window_limit_reached: bool,
+    pub(crate) token_limit_reached: bool,
+}
+
+impl ContextWindowTokenStatus {
+    pub(crate) fn tokens_until_compaction(&self) -> i64 {
+        let full_context_remaining = self.full_context_window_limit.map_or(i64::MAX, |limit| {
+            limit.saturating_sub(self.active_context_tokens)
+        });
+        self.auto_compact_scope_limit
+            .saturating_sub(self.auto_compact_scope_tokens)
+            .min(full_context_remaining)
+            .max(0)
+    }
+}
+
+pub(crate) async fn context_window_token_status(
+    sess: &Session,
+    turn_context: &TurnContext,
+) -> ContextWindowTokenStatus {
+    let active_context_tokens = sess.get_total_token_usage().await;
+    let mut auto_compact_window_prefill_tokens = None;
+    let (auto_compact_scope_tokens, auto_compact_scope_limit, full_context_window_limit) =
+        match turn_context.config.model_auto_compact_token_limit_scope {
+            AutoCompactTokenLimitScope::Total => (
+                active_context_tokens,
+                turn_context
+                    .model_info
+                    .auto_compact_token_limit()
+                    .unwrap_or(i64::MAX),
+                None,
+            ),
+            AutoCompactTokenLimitScope::BodyAfterPrefix => {
+                let window = sess.auto_compact_window_snapshot().await;
+                auto_compact_window_prefill_tokens = window.prefill_input_tokens;
+                let baseline = window.prefill_input_tokens.unwrap_or(active_context_tokens);
+                (
+                    active_context_tokens.saturating_sub(baseline),
+                    turn_context
+                        .config
+                        .model_auto_compact_token_limit
+                        .or_else(|| turn_context.model_info.auto_compact_token_limit())
+                        .unwrap_or(i64::MAX),
+                    turn_context.model_context_window(),
+                )
+            }
+        };
+    let full_context_window_limit_reached =
+        full_context_window_limit.is_some_and(|full_context_window_limit| {
+            active_context_tokens >= full_context_window_limit
+        });
+    let token_limit_reached =
+        auto_compact_scope_tokens >= auto_compact_scope_limit || full_context_window_limit_reached;
+    ContextWindowTokenStatus {
+        active_context_tokens,
+        auto_compact_scope_tokens,
+        auto_compact_scope_limit,
+        full_context_window_limit,
+        auto_compact_window_prefill_tokens,
+        full_context_window_limit_reached,
+        token_limit_reached,
+    }
+}