Account for token usage from incomplete responses (#53670)

## Why

Terminal `response.incomplete` errors discard reported token usage. Counting that usage as a new context baseline can also double-count input and trigger unnecessary compaction on the next turn.

## What changed

- Carry the response ID and valid reported usage with incomplete-response errors.
- Record usage for sampling and foreground compaction in cumulative totals, rollout records, budgets, and token-usage contributors without replacing the context baseline. Preserve the original terminal error, including when accounting exhausts the budget or cancellation races the error.
- Charge incomplete background compaction requests to the rollout budget without publishing foreground token usage.
- Ignore missing or malformed usage rather than estimating it.

## Testing

Extend coverage for SSE and WebSocket incomplete responses, rollout usage records, compaction accounting, deferred token-count events, and token-usage contributors. Add regressions for unnecessary compaction on the next turn and background compaction publishing foreground usage.

GitOrigin-RevId: bf1ee6df3912052ab7c19e1c6af8ad3dc4b07675

codex-rs/codex-api/src/error.rs

@@ -1,6 +1,7 @@
 use crate::rate_limits::RateLimitError;
 use codex_client::TransportError;
 use codex_http_client::RetryAfter;
+use codex_protocol::error::ResponseIncompleteError;
 use codex_protocol::protocol::MisalignmentErrorDetails;
 use http::StatusCode;
 use serde_json::Value;
@@ -16,8 +17,8 @@ pub enum ApiError {
     Stream(String),
     #[error("stream error: Incomplete response returned, reason: content_filter")]
     ContentFilter,
-    #[error("Incomplete response returned, reason: {0}")]
-    ResponseIncomplete(String),
+    #[error(transparent)]
+    ResponseIncomplete(Box<ResponseIncompleteError>),
     #[error("context window exceeded")]
     ContextWindowExceeded,
     #[error("quota exceeded")]