实现 Direct replay 有界滑动窗口

DirectProject replay 按上下文预算保留最新连续历史

超预算时仅派生裁剪 prompt，不修改 project.jsonl

补充超大历史与当前请求超限测试

apps/ai-game-creator-shell/src-tauri/src/agent/codex_app_server.rs

@@ -2125,16 +2125,18 @@ impl CodexAppServerConnection {
         let thread_id = thread_lease.thread_id.clone();
         let mut request = request;
         if thread_created && self.inner.workspace_mode.uses_direct_conversation() {
-            // DirectProject intentionally replays the complete append-only
-            // project history.  AGC owns that durable fact source; keeping
-            // the replay lossless is the product contract even though a
-            // future context-budget policy may need to change this choice.
+            // DirectProject owns the append-only project history in AGC.  The
+            // replay builder derives a bounded prompt without mutating that
+            // durable fact source, so a new ephemeral thread can recover the
+            // newest contiguous context within the model budget.
             let current_prompt = direct_codex_current_user_prompt(&request).to_string();
             let history_root = direct_history_root.unwrap_or(&self.inner.workspace_path);
             let history_prompt = build_direct_codex_history_prompt(
                 history_root,
                 direct_client_turn_id.unwrap_or("__none__"),
                 &current_prompt,
+                &request,
+                llm,
             )
             .map_err(platform_llm::LlmError::InvalidRequest)?;
             if let Some(message) = request
@@ -3217,24 +3219,153 @@ pub(crate) async fn direct_game_creator_codex_chat_at_with_optional_observer(
         .map_err(|error| error.to_string())
 }
 
+/// Builds the prompt used when a new DirectProject thread needs replay.
+///
+/// The JSONL history remains immutable; only the derived prompt is bounded.
+/// When the full request exceeds the replay target, the oldest contiguous
+/// records are omitted and a plain `system:` marker is prepended.
 pub(crate) fn build_direct_codex_history_prompt(
     root: &std::path::Path,
     client_turn_id: &str,
     current_prompt: &str,
+    base_request: &LlmRunRequest,
+    llm: &GameCreatorLlmConfig,
 ) -> Result<String, String> {
     let conversation = read_local_conversation_for_session_at(root, None, None)?;
     let current_message_id = format!("direct-codex:{client_turn_id}:user");
     // The deliberately simple role-prefix format is part of the Direct
     // replay contract.  Do not introduce an envelope or implicit escaping
     // here without updating the persisted-history compatibility decision.
-    let mut lines = conversation
+    let lines = conversation
         .messages
         .iter()
         .filter(|message| message.message_id.as_deref() != Some(current_message_id.as_str()))
         .map(|message| format!("{}: {}", message.role, message.content))
         .collect::<Vec<_>>();
-    lines.push(format!("user: {}", current_prompt.trim()));
-    Ok(lines.join("\n"))
+    let current_line = format!("user: {}", current_prompt.trim());
+    let full_prompt = format_direct_codex_replay_prompt(&lines, &current_line, None);
+    let target_budget = direct_codex_replay_target_budget(llm, base_request)?;
+    if direct_codex_replay_prompt_fits(base_request, llm, &full_prompt, target_budget)? {
+        return Ok(full_prompt);
+    }
+
+    // The persisted project conversation is immutable.  We only derive a
+    // bounded prompt for this replay, keeping the newest contiguous records.
+    let omission_marker = DIRECT_CODEX_REPLAY_OMISSION_MARKER;
+    let mut selected_reversed = Vec::new();
+    for line in lines.iter().rev() {
+        let mut candidate_reversed = selected_reversed.clone();
+        candidate_reversed.push(line.as_str());
+        let candidate_lines = candidate_reversed.iter().rev().copied().collect::<Vec<_>>();
+        let candidate_prompt = format_direct_codex_replay_prompt(
+            &candidate_lines,
+            &current_line,
+            Some(omission_marker),
+        );
+        if direct_codex_replay_prompt_fits(base_request, llm, &candidate_prompt, target_budget)? {
+            selected_reversed.push(line.as_str());
+        } else {
+            break;
+        }
+    }
+
+    let selected_lines = selected_reversed.iter().rev().copied().collect::<Vec<_>>();
+    let marked_prompt =
+        format_direct_codex_replay_prompt(&selected_lines, &current_line, Some(omission_marker));
+    if direct_codex_replay_prompt_fits(base_request, llm, &marked_prompt, target_budget)? {
+        return Ok(marked_prompt);
+    }
+
+    // If the marker itself would push the request over the target, preserve
+    // the current user request and omit only the marker.
+    let current_only_prompt =
+        format_direct_codex_replay_prompt(&[] as &[&str], &current_line, None);
+    if direct_codex_replay_prompt_fits(base_request, llm, &current_only_prompt, target_budget)? {
+        return Ok(current_only_prompt);
+    }
+    direct_codex_replay_validate_context_budget(base_request, llm, &current_only_prompt)
+}
+
+const DIRECT_CODEX_REPLAY_OMISSION_MARKER: &str =
+    "system: Earlier conversation history was omitted due to context budget.";
+
+fn format_direct_codex_replay_prompt(
+    history_lines: &[impl AsRef<str>],
+    current_line: &str,
+    omission_marker: Option<&str>,
+) -> String {
+    let mut lines = Vec::with_capacity(history_lines.len() + 2);
+    if let Some(marker) = omission_marker {
+        lines.push(marker.to_string());
+    }
+    lines.extend(history_lines.iter().map(|line| line.as_ref().to_string()));
+    lines.push(current_line.to_string());
+    lines.join("\n")
+}
+
+fn direct_codex_replay_target_budget(
+    llm: &GameCreatorLlmConfig,
+    request: &LlmRunRequest,
+) -> Result<u64, String> {
+    const SAFETY_MARGIN_TOKENS: u64 = 4_096;
+    let max_output_tokens = u64::from(request.max_output_tokens.unwrap_or(0));
+    let hard_budget = llm
+        .context_window_tokens
+        .checked_sub(max_output_tokens)
+        .and_then(|value| value.checked_sub(SAFETY_MARGIN_TOKENS))
+        .ok_or_else(|| "Direct replay 没有可用的输入上下文预算".to_string())?;
+    Ok(llm.auto_compact_token_limit.min(hard_budget))
+}
+
+fn direct_codex_replay_estimate(
+    base_request: &LlmRunRequest,
+    prompt: &str,
+) -> Result<LlmRunRequest, String> {
+    let mut request = base_request.clone();
+    let user = request
+        .messages
+        .iter_mut()
+        .rev()
+        .find(|message| message.role == LlmMessageRole::User)
+        .ok_or_else(|| "Direct replay 请求缺少 user message".to_string())?;
+    user.content = prompt.to_string();
+    Ok(request)
+}
+
+fn direct_codex_replay_prompt_fits(
+    base_request: &LlmRunRequest,
+    llm: &GameCreatorLlmConfig,
+    prompt: &str,
+    target_budget: u64,
+) -> Result<bool, String> {
+    let request = direct_codex_replay_estimate(base_request, prompt)?;
+    let estimated = estimate_game_creator_llm_request_tokens(&request)?;
+    if estimated > target_budget {
+        return Ok(false);
+    }
+    validate_game_creator_llm_request_context_budget(
+        llm,
+        &request,
+        estimated,
+        "Direct replay 请求",
+    )?;
+    Ok(true)
+}
+
+fn direct_codex_replay_validate_context_budget(
+    base_request: &LlmRunRequest,
+    llm: &GameCreatorLlmConfig,
+    prompt: &str,
+) -> Result<String, String> {
+    let request = direct_codex_replay_estimate(base_request, prompt)?;
+    let estimated = estimate_game_creator_llm_request_tokens(&request)?;
+    validate_game_creator_llm_request_context_budget(
+        llm,
+        &request,
+        estimated,
+        "Direct replay 请求",
+    )?;
+    Ok(prompt.to_string())
 }
 
 /// Direct home-page chat never binds Codex to a user project.  It gets a
@@ -3349,14 +3480,92 @@ mod tests {
             )
             .expect("append history");
         }
-        let prompt = build_direct_codex_history_prompt(root.path(), "new-turn", "new request")
-            .expect("build prompt");
+        let request = LlmRunRequest::single_turn("system", "new request")
+            .with_model("fixture-model")
+            .with_max_output_tokens(16_000);
+        let prompt = build_direct_codex_history_prompt(
+            root.path(),
+            "new-turn",
+            "new request",
+            &request,
+            &test_llm(),
+        )
+        .expect("build prompt");
         assert_eq!(
             prompt,
             "user: hello\nassistant: partial\nunexpected interrupt happened here\ntool: file-read result\nuser: new request"
         );
     }
 
+    #[test]
+    fn direct_history_prompt_slides_old_prefix_when_budget_is_exceeded() {
+        let root = tempfile::tempdir().expect("temp dir");
+        init_local_game_project_at(root.path(), "window-project", "window").expect("init");
+        for (role, content, message_id) in [
+            ("user", "old ".repeat(1_000), "old-user"),
+            ("assistant", "middle ".repeat(100), "middle-assistant"),
+            ("tool", "newest ".repeat(100), "newest-tool"),
+        ] {
+            append_local_conversation_message_for_session_idempotent_at(
+                root.path(),
+                None,
+                None,
+                LocalConversationMessage {
+                    role: role.to_string(),
+                    content,
+                    agent_id: None,
+                },
+                message_id,
+            )
+            .expect("append history");
+        }
+        let mut llm = test_llm();
+        llm.auto_compact_token_limit = 800;
+        let request = LlmRunRequest::single_turn("system", "new request")
+            .with_model("fixture-model")
+            .with_max_output_tokens(16_000);
+        let before =
+            std::fs::read_to_string(root.path().join(".agent/conversations/project.jsonl"))
+                .expect("read history");
+        let prompt = build_direct_codex_history_prompt(
+            root.path(),
+            "new-turn",
+            "new request",
+            &request,
+            &llm,
+        )
+        .expect("build prompt");
+        let after = std::fs::read_to_string(root.path().join(".agent/conversations/project.jsonl"))
+            .expect("read history");
+
+        assert!(prompt.starts_with(DIRECT_CODEX_REPLAY_OMISSION_MARKER));
+        assert!(prompt.contains("tool: newest"));
+        assert!(!prompt.contains("user: old"));
+        assert!(prompt.ends_with("user: new request"));
+        assert_eq!(before, after);
+    }
+
+    #[test]
+    fn direct_history_prompt_rejects_current_request_that_exceeds_context() {
+        let root = tempfile::tempdir().expect("temp dir");
+        init_local_game_project_at(root.path(), "oversized-project", "oversized").expect("init");
+        let mut llm = test_llm();
+        llm.context_window_tokens = 5_000;
+        llm.auto_compact_token_limit = 1_000;
+        let request = LlmRunRequest::single_turn("system", "new request")
+            .with_model("fixture-model")
+            .with_max_output_tokens(100);
+        let error = build_direct_codex_history_prompt(
+            root.path(),
+            "new-turn",
+            &"request ".repeat(10_000),
+            &request,
+            &llm,
+        )
+        .expect_err("oversized request should fail");
+        assert!(error.contains("Direct replay 请求"));
+    }
+
     #[test]
     fn direct_item_activities_are_closed_safe_categories() {
         let allowed = [