[codex] add memory extensions (#16276)

# External (non-OpenAI) Pull Request Requirements

Before opening this Pull Request, please read the dedicated
"Contributing" markdown file or your PR may be closed:
https://github.com/openai/codex/blob/main/docs/contributing.md

If your PR conforms to our contribution guidelines, replace this text
with a detailed and high quality description of your changes.

Include a link to a bug report or enhancement request.

codex-rs/core/src/memories/mod.rs

@@ -25,6 +25,7 @@ pub(crate) use control::clear_memory_root_contents;
 pub(crate) use start::start_memories_startup_task;
 
 mod artifacts {
+    pub(super) const EXTENSIONS_SUBDIR: &str = "memories_extensions";
     pub(super) const ROLLOUT_SUMMARIES_SUBDIR: &str = "rollout_summaries";
     pub(super) const RAW_MEMORIES_FILENAME: &str = "raw_memories.md";
 }
@@ -106,6 +107,10 @@ fn rollout_summaries_dir(root: &Path) -> PathBuf {
     root.join(artifacts::ROLLOUT_SUMMARIES_SUBDIR)
 }
 
+fn memory_extensions_root(root: &Path) -> PathBuf {
+    root.with_file_name(artifacts::EXTENSIONS_SUBDIR)
+}
+
 fn raw_memories_file(root: &Path) -> PathBuf {
     root.join(artifacts::RAW_MEMORIES_FILENAME)
 }

codex-rs/core/src/memories/prompts.rs

@@ -1,3 +1,4 @@
+use crate::memories::memory_extensions_root;
 use crate::memories::memory_root;
 use crate::memories::phase_one;
 use crate::memories::storage::rollout_summary_file_stem_from_parts;
@@ -31,6 +32,18 @@ static MEMORY_TOOL_DEVELOPER_INSTRUCTIONS_TEMPLATE: LazyLock<Template> = LazyLoc
         "memories/read_path.md",
     )
 });
+static MEMORY_EXTENSIONS_FOLDER_STRUCTURE_TEMPLATE: LazyLock<Template> = LazyLock::new(|| {
+    parse_embedded_template(
+        MEMORY_EXTENSIONS_FOLDER_STRUCTURE,
+        "memories/extensions_folder_structure.md",
+    )
+});
+static MEMORY_EXTENSIONS_PRIMARY_INPUTS_TEMPLATE: LazyLock<Template> = LazyLock::new(|| {
+    parse_embedded_template(
+        MEMORY_EXTENSIONS_PRIMARY_INPUTS,
+        "memories/extensions_primary_inputs.md",
+    )
+});
 
 fn parse_embedded_template(source: &'static str, template_name: &str) -> Template {
     match Template::parse(source) {
@@ -39,24 +52,82 @@ fn parse_embedded_template(source: &'static str, template_name: &str) -> Templat
     }
 }
 
+const MEMORY_EXTENSIONS_FOLDER_STRUCTURE: &str = r#"
+Memory extensions (under {{ memory_extensions_root }}/):
+
+- <extension_name>/instructions.md
+  - Source-specific guidance for interpreting additional memory signals. If an
+    extension folder exists, you must read its instructions.md to determine how to use this memory
+    source.
+
+If the user has any memory extensions, you MUST read the instructions for each extension to
+determine how to use the memory source. If it has no extension folders, continue with the standard
+memory inputs only.
+"#;
+
+const MEMORY_EXTENSIONS_PRIMARY_INPUTS: &str = r#"
+Optional source-specific inputs:
+Under `{{ memory_extensions_root }}/`:
+
+- `<extension_name>/instructions.md`
+  - If extension folders exist, read each instructions.md first and follow it when interpreting
+    that extension's memory source.
+"#;
+
 /// Builds the consolidation subagent prompt for a specific memory root.
 pub(super) fn build_consolidation_prompt(
     memory_root: &Path,
     selection: &Phase2InputSelection,
 ) -> String {
+    let memory_extensions_root = memory_extensions_root(memory_root);
+    let memory_extensions_exist = memory_extensions_root.is_dir();
     let memory_root = memory_root.display().to_string();
+    let memory_extensions_root = memory_extensions_root.display().to_string();
+    let memory_extensions_folder_structure = if memory_extensions_exist {
+        render_memory_extensions_block(
+            &MEMORY_EXTENSIONS_FOLDER_STRUCTURE_TEMPLATE,
+            &memory_extensions_root,
+        )
+    } else {
+        String::new()
+    };
+    let memory_extensions_primary_inputs = if memory_extensions_exist {
+        render_memory_extensions_block(
+            &MEMORY_EXTENSIONS_PRIMARY_INPUTS_TEMPLATE,
+            &memory_extensions_root,
+        )
+    } else {
+        String::new()
+    };
     let phase2_input_selection = render_phase2_input_selection(selection);
     CONSOLIDATION_PROMPT_TEMPLATE
         .render([
             ("memory_root", memory_root.as_str()),
+            (
+                "memory_extensions_folder_structure",
+                memory_extensions_folder_structure.as_str(),
+            ),
+            (
+                "memory_extensions_primary_inputs",
+                memory_extensions_primary_inputs.as_str(),
+            ),
             ("phase2_input_selection", phase2_input_selection.as_str()),
         ])
         .unwrap_or_else(|err| {
-        warn!("failed to render memories consolidation prompt template: {err}");
-        format!(
-            "## Memory Phase 2 (Consolidation)\nConsolidate Codex memories in: {memory_root}\n\n{phase2_input_selection}"
-        )
-    })
+            warn!("failed to render memories consolidation prompt template: {err}");
+            format!(
+                "## Memory Phase 2 (Consolidation)\nConsolidate Codex memories in: {memory_root}\n\n{phase2_input_selection}"
+            )
+        })
+}
+
+fn render_memory_extensions_block(template: &Template, memory_extensions_root: &str) -> String {
+    template
+        .render([("memory_extensions_root", memory_extensions_root)])
+        .unwrap_or_else(|err| {
+            warn!("failed to render memories extension prompt block: {err}");
+            String::new()
+        })
 }
 
 fn render_phase2_input_selection(selection: &Phase2InputSelection) -> String {

codex-rs/core/src/memories/prompts_tests.rs

@@ -55,14 +55,56 @@ fn build_stage_one_input_message_uses_default_limit_when_model_context_window_mi
 
 #[test]
 fn build_consolidation_prompt_renders_embedded_template() {
-    let prompt =
-        build_consolidation_prompt(Path::new("/tmp/memories"), &Phase2InputSelection::default());
+    let temp = tempdir().unwrap();
+    let memories_dir = temp.path().join("memories");
 
-    assert!(prompt.contains("Folder structure (under /tmp/memories/):"));
+    let prompt = build_consolidation_prompt(&memories_dir, &Phase2InputSelection::default());
+
+    assert!(prompt.contains(&format!(
+        "Folder structure (under {}/):",
+        memories_dir.display()
+    )));
+    assert!(!prompt.contains("Memory extensions (under"));
+    assert!(!prompt.contains("<extension_name>/instructions.md"));
     assert!(prompt.contains("**Diff since last consolidation:**"));
     assert!(prompt.contains("- selected inputs this run: 0"));
 }
 
+#[tokio::test]
+async fn build_consolidation_prompt_points_to_extensions_without_inlining_them() {
+    let temp = tempdir().unwrap();
+    let memories_dir = temp.path().join("memories");
+    let extension_dir = temp.path().join("memories_extensions/tape_recorder");
+    tokio_fs::create_dir_all(extension_dir.join("resources"))
+        .await
+        .unwrap();
+    tokio_fs::write(
+        extension_dir.join("instructions.md"),
+        "source-specific instructions\n",
+    )
+    .await
+    .unwrap();
+    tokio_fs::write(
+        extension_dir.join("resources/notes.md"),
+        "source-specific resource\n",
+    )
+    .await
+    .unwrap();
+
+    let prompt = build_consolidation_prompt(&memories_dir, &Phase2InputSelection::default());
+    let memory_extensions_dir = temp.path().join("memories_extensions");
+
+    assert!(prompt.contains(&format!(
+        "Memory extensions (under {}/)",
+        memory_extensions_dir.display()
+    )));
+    assert!(prompt.contains(&format!("Under `{}/`:", memory_extensions_dir.display())));
+    assert!(prompt.contains("<extension_name>/instructions.md"));
+    assert!(prompt.contains("Optional source-specific inputs:"));
+    assert!(!prompt.contains("source-specific instructions"));
+    assert!(!prompt.contains("source-specific resource"));
+}
+
 #[tokio::test]
 async fn build_memory_tool_developer_instructions_renders_embedded_template() {
     let temp = tempdir().unwrap();

codex-rs/core/templates/memories/consolidation.md

@@ -33,7 +33,7 @@ Folder structure (under {{ memory_root }}/):
   - Recap of the rollout, including lessons learned, reusable knowledge,
     pointers/references, and pruned raw evidence snippets. Distilled version of
     everything valuable from the raw rollout.
-
+{{ memory_extensions_folder_structure }}
 ============================================================
 GLOBAL SAFETY, HYGIENE, AND NO-FILLER RULES (STRICT)
 ============================================================
@@ -135,7 +135,7 @@ Under `{{ memory_root }}/`:
   - read the existing summary so updates stay consistent
 - `skills/*`
   - read existing skills so updates are incremental and non-duplicative
-
+{{ memory_extensions_primary_inputs }}
 Mode selection:
 
 - INIT phase: existing artifacts are missing/empty (especially `memory_summary.md`