Add a partial answer message phase (#51241)

## Why

Assistant answer text may be followed by more output or tools. A distinct `partial_answer` phase lets callers represent this separately from commentary and a terminal `final_answer`.

## What changed

- Add `MessagePhase::PartialAnswer` and expose `partial_answer` in the app-server schemas and generated TypeScript and Python types.
- Keep the TUI working indicator visible after partial answers and exclude them from the thread history's final-answer summary field.
- Route partial answers to the speakable channel in realtime V3 BEM-tag mode.

## Testing

Add coverage for phase preservation through serialization, input-message conversion, and SSE item start/completion events. Extend TUI snapshot coverage to verify that partial answers keep the working indicator visible while final answers hide it.

GitOrigin-RevId: 1ae3ad9264b6e36ae1cbe6b93df3d345ab4460e6

codex-rs/app-server-protocol/schema/json/ClientRequest.json

@@ -2213,7 +2213,7 @@
       "type": "string"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -2223,7 +2223,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/ServerNotification.json

@@ -3015,7 +3015,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -3025,7 +3025,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -15361,7 +15361,7 @@
         "type": "string"
       },
       "MessagePhase": {
-        "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+        "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
         "oneOf": [
           {
             "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -15371,7 +15371,14 @@
             "type": "string"
           },
           {
-            "description": "The assistant's terminal answer text for the current turn.",
+            "description": "Stable answer text that may be followed by more assistant output or tools.",
+            "enum": [
+              "partial_answer"
+            ],
+            "type": "string"
+          },
+          {
+            "description": "The assistant's declared terminal answer text for the current turn.",
             "enum": [
               "final_answer"
             ],

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -11373,7 +11373,7 @@
       "type": "string"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -11383,7 +11383,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ItemCompletedNotification.json

@@ -650,7 +650,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -660,7 +660,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ItemStartedNotification.json

@@ -650,7 +650,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -660,7 +660,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/RawResponseItemCompletedNotification.json

@@ -389,7 +389,7 @@
       "type": "string"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -399,7 +399,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ReviewStartResponse.json

@@ -798,7 +798,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -808,7 +808,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadForkResponse.json

@@ -902,7 +902,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -912,7 +912,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadItemsListResponse.json

@@ -650,7 +650,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -660,7 +660,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadListResponse.json

@@ -824,7 +824,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -834,7 +834,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadMetadataUpdateResponse.json

@@ -824,7 +824,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -834,7 +834,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadReadResponse.json

@@ -824,7 +824,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -834,7 +834,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadResumeParams.json

@@ -451,7 +451,7 @@
       "type": "string"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -461,7 +461,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadResumeResponse.json

@@ -918,7 +918,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -928,7 +928,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadRevertResponse.json

@@ -824,7 +824,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -834,7 +834,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadStartResponse.json

@@ -902,7 +902,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -912,7 +912,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadStartedNotification.json

@@ -824,7 +824,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -834,7 +834,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadTurnsListResponse.json

@@ -798,7 +798,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -808,7 +808,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/ThreadUnarchiveResponse.json

@@ -824,7 +824,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -834,7 +834,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/TurnCompletedNotification.json

@@ -798,7 +798,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -808,7 +808,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/TurnStartResponse.json

@@ -798,7 +798,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -808,7 +808,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/json/v2/TurnStartedNotification.json

@@ -798,7 +798,7 @@
       "type": "object"
     },
     "MessagePhase": {
-      "description": "Classifies an assistant message as interim commentary or final answer text.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
+      "description": "Classifies assistant text as commentary, a partial answer, or a terminal answer.\n\nProviders do not emit this consistently, so callers must treat `None` as \"phase unknown\" and keep compatibility behavior for legacy models.",
       "oneOf": [
         {
           "description": "Mid-turn assistant text (for example preamble/progress narration).\n\nAdditional tool calls or assistant output may follow before turn completion.",
@@ -808,7 +808,14 @@
           "type": "string"
         },
         {
-          "description": "The assistant's terminal answer text for the current turn.",
+          "description": "Stable answer text that may be followed by more assistant output or tools.",
+          "enum": [
+            "partial_answer"
+          ],
+          "type": "string"
+        },
+        {
+          "description": "The assistant's declared terminal answer text for the current turn.",
           "enum": [
             "final_answer"
           ],

codex-rs/app-server-protocol/schema/typescript/MessagePhase.ts

@@ -3,9 +3,9 @@
 // This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
 
 /**
- * Classifies an assistant message as interim commentary or final answer text.
+ * Classifies assistant text as commentary, a partial answer, or a terminal answer.
  *
  * Providers do not emit this consistently, so callers must treat `None` as
  * "phase unknown" and keep compatibility behavior for legacy models.
  */
-export type MessagePhase = "commentary" | "final_answer";
+export type MessagePhase = "commentary" | "partial_answer" | "final_answer";

codex-rs/codex-api/src/sse/responses.rs

@@ -734,6 +734,46 @@ mod tests {
         Duration::from_millis(1000)
     }
 
+    #[tokio::test]
+    async fn partial_answer_phase_survives_item_start_and_completion() {
+        let item = json!({
+            "id": "msg_partial",
+            "type": "message",
+            "role": "assistant",
+            "content": [],
+            "phase": "partial_answer"
+        });
+        let added = json!({"type": "response.output_item.added", "item": item});
+        let delta = json!({"type": "response.output_text.delta", "delta": "First result."});
+        let mut done_item = item;
+        done_item["content"] = json!([{"type": "output_text", "text": "First result."}]);
+        let done = json!({"type": "response.output_item.done", "item": done_item});
+        let completed = json!({
+            "type": "response.completed",
+            "response": {"id": "resp1", "end_turn": false}
+        });
+        let stream = [added, delta, done, completed]
+            .into_iter()
+            .map(|event| format!("data: {event}\n\n"))
+            .collect::<String>();
+
+        let events = collect_events(&[stream.as_bytes()]).await;
+        assert_matches!(events.as_slice(), [
+            Ok(ResponseEvent::OutputItemAdded(ResponseItem::Message {
+                phase: Some(MessagePhase::PartialAnswer), content: start_content, ..
+            })),
+            Ok(ResponseEvent::OutputTextDelta(text)),
+            Ok(ResponseEvent::OutputItemDone(ResponseItem::Message {
+                phase: Some(MessagePhase::PartialAnswer), content: done_content, ..
+            })),
+            Ok(ResponseEvent::Completed { end_turn: Some(false), .. }),
+        ] if start_content.is_empty()
+            && text == "First result."
+            && done_content == &vec![codex_protocol::models::ContentItem::OutputText {
+                text: "First result.".to_string()
+            }]);
+    }
+
     #[tokio::test]
     async fn parses_items_and_completed() {
         let item1 = json!({

codex-rs/core/src/realtime_conversation.rs

@@ -928,6 +928,8 @@ impl RealtimeConversationManager {
         if handoff.client_managed_handoffs {
             return Ok(());
         }
+        // TODO: Preserve explicit PartialAnswer phases through completed and streamed BEM
+        // routing, with integration coverage asserting the speakable channel.
         let phase = if handoff.routes_handoff_by_bem() {
             match bem_message_phase(
                 &output_text,
@@ -942,6 +944,8 @@ impl RealtimeConversationManager {
         } else {
             phase
         };
+        // TODO: Treat PartialAnswer as nonterminal for V1 handoffs, omitting the final-message
+        // prefix for streamed, completed-item, and standalone output.
         let is_commentary = matches!(phase, Some(MessagePhase::Commentary));
         let active_handoff = handoff.stream.lock().await.active_handoff.clone();
         let output = match active_handoff {
@@ -2272,7 +2276,9 @@ fn v3_output_writer(
         CodexResponseHandoffMode::Thinking => None,
         CodexResponseHandoffMode::Commentary => Some(RealtimeContextAppendChannel::Commentary),
         CodexResponseHandoffMode::BemTags => match phase {
-            Some(MessagePhase::FinalAnswer) => Some(RealtimeContextAppendChannel::Speakable),
+            Some(MessagePhase::PartialAnswer | MessagePhase::FinalAnswer) => {
+                Some(RealtimeContextAppendChannel::Speakable)
+            }
             Some(MessagePhase::Commentary) => Some(RealtimeContextAppendChannel::Commentary),
             None => Some(RealtimeContextAppendChannel::Speakable),
         },

codex-rs/core/src/session/turn.rs

@@ -2750,6 +2750,8 @@ async fn try_run_sampling_request(
                     cancellation_token: cancellation_token.child_token(),
                 };
 
+                // TODO: Allow mailbox preemption after PartialAnswer and keep delivery open
+                // in the completed-item deferral predicates.
                 let preempt_for_mailbox_mail = match &item {
                     ResponseItem::Message { role, phase, .. } => {
                         role == "assistant" && matches!(phase, Some(MessagePhase::Commentary))

codex-rs/protocol/src/models.rs

@@ -937,7 +937,7 @@ pub const DEFAULT_IMAGE_DETAIL: ImageDetail = ImageDetail::High;
 
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, JsonSchema, TS)]
 #[serde(rename_all = "snake_case")]
-/// Classifies an assistant message as interim commentary or final answer text.
+/// Classifies assistant text as commentary, a partial answer, or a terminal answer.
 ///
 /// Providers do not emit this consistently, so callers must treat `None` as
 /// "phase unknown" and keep compatibility behavior for legacy models.
@@ -947,7 +947,9 @@ pub enum MessagePhase {
     /// Additional tool calls or assistant output may follow before turn
     /// completion.
     Commentary,
-    /// The assistant's terminal answer text for the current turn.
+    /// Stable answer text that may be followed by more assistant output or tools.
+    PartialAnswer,
+    /// The assistant's declared terminal answer text for the current turn.
     FinalAnswer,
 }
 
@@ -2518,27 +2520,38 @@ mod tests {
     }
 
     #[test]
-    fn response_input_message_conversion_preserves_phase() {
-        let item = ResponseItem::from(ResponseInputItem::Message {
-            role: "assistant".to_string(),
-            content: vec![ContentItem::OutputText {
-                text: "still working".to_string(),
-            }],
-            phase: Some(MessagePhase::Commentary),
-        });
-
-        assert_eq!(
-            item,
-            ResponseItem::Message {
+    fn response_input_message_conversion_preserves_phase() -> Result<()> {
+        for phase in [
+            None,
+            Some(MessagePhase::Commentary),
+            Some(MessagePhase::PartialAnswer),
+            Some(MessagePhase::FinalAnswer),
+        ] {
+            let input = ResponseInputItem::Message {
+                role: "assistant".to_string(),
+                content: vec![ContentItem::OutputText {
+                    text: "answer text".to_string(),
+                }],
+                phase: phase.clone(),
+            };
+            let wire = serde_json::to_value(input)?;
+            let item = ResponseItem::from(serde_json::from_value::<ResponseInputItem>(wire)?);
+            let expected = ResponseItem::Message {
                 id: None,
                 role: "assistant".to_string(),
                 content: vec![ContentItem::OutputText {
-                    text: "still working".to_string(),
+                    text: "answer text".to_string(),
                 }],
-                phase: Some(MessagePhase::Commentary),
+                phase,
                 internal_chat_message_metadata_passthrough: None,
-            }
-        );
+            };
+            assert_eq!(item, expected);
+            assert_eq!(
+                serde_json::from_value::<ResponseItem>(serde_json::to_value(item)?)?,
+                expected
+            );
+        }
+        Ok(())
     }
 
     #[test]

codex-rs/thread-store/src/local/thread_history.rs

@@ -520,7 +520,7 @@ WHERE thread_id = ?
                 .map_err(thread_history_error)?;
             }
             ThreadItem::AgentMessage {
-                phase: Some(MessagePhase::Commentary) | None,
+                phase: Some(MessagePhase::Commentary | MessagePhase::PartialAnswer) | None,
                 ..
             }
             | ThreadItem::HookPrompt { .. }

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__single_line_partial_answer_keeps_working_status.snap

@@ -0,0 +1,14 @@
+---
+source: tui/src/chatwidget/tests/status_and_layout.rs
+expression: normalize_snapshot_paths(terminal.backend().vt100().screen().contents())
+---
+
+
+• 1
+
+• Working (0s • esc to interrupt)
+
+
+› Ask Codex to do anything
+
+  gpt-5 default · /tmp/project

codex-rs/tui/src/chatwidget/streaming.rs

@@ -482,7 +482,7 @@ impl ChatWidget {
                 Some(MessagePhase::FinalAnswer) | None => {
                     !self.input_queue.pending_steers.is_empty()
                 }
-                Some(MessagePhase::Commentary) => true,
+                Some(MessagePhase::Commentary | MessagePhase::PartialAnswer) => true,
             };
         self.maybe_restore_status_indicator_after_stream_idle();
     }

codex-rs/tui/src/chatwidget/tests/status_and_layout.rs

@@ -2205,42 +2205,51 @@ async fn streaming_final_answer_keeps_task_running_state() {
 }
 
 #[tokio::test]
-async fn single_line_final_answer_hides_working_status_snapshot() {
-    let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
-    chat.thread_id = Some(ThreadId::new());
+async fn answer_phase_controls_working_status_snapshot() {
+    for (phase, working_visible, snapshot) in [
+        (
+            MessagePhase::FinalAnswer,
+            false,
+            "single_line_final_answer_hides_working_status",
+        ),
+        (
+            MessagePhase::PartialAnswer,
+            true,
+            "single_line_partial_answer_keeps_working_status",
+        ),
+    ] {
+        let (mut chat, mut rx, _op_rx) = make_chatwidget_manual(Some("gpt-5")).await;
+        chat.thread_id = Some(ThreadId::new());
 
-    complete_user_message(&mut chat, "user-1", "count to 1");
-    chat.on_task_started();
-    complete_assistant_message(
-        &mut chat,
-        "msg-final-single-line",
-        "1",
-        Some(MessagePhase::FinalAnswer),
-    );
+        complete_user_message(&mut chat, "user-1", "count to 1");
+        chat.on_task_started();
+        complete_assistant_message(&mut chat, "msg-final-single-line", "1", Some(phase));
 
-    assert!(chat.bottom_pane.is_task_running());
-    assert!(!chat.bottom_pane.status_indicator_visible());
+        assert!(chat.bottom_pane.is_task_running());
+        assert_eq!(chat.bottom_pane.status_indicator_visible(), working_visible);
 
-    let width: u16 = 40;
-    let vt_height: u16 = 10;
-    let ui_height = chat.desired_height(width);
-    let viewport = Rect::new(0, vt_height - ui_height - 1, width, ui_height);
-    let backend = VT100Backend::new(width, vt_height);
-    let mut terminal = crate::custom_terminal::Terminal::with_options(backend).expect("terminal");
-    terminal.set_viewport_area(viewport);
+        let width: u16 = 40;
+        let vt_height: u16 = 10;
+        let ui_height = chat.desired_height(width);
+        let viewport = Rect::new(0, vt_height - ui_height - 1, width, ui_height);
+        let backend = VT100Backend::new(width, vt_height);
+        let mut terminal =
+            crate::custom_terminal::Terminal::with_options(backend).expect("terminal");
+        terminal.set_viewport_area(viewport);
 
-    for lines in drain_insert_history(&mut rx) {
-        crate::insert_history::insert_history_lines(&mut terminal, lines)
-            .expect("insert history lines");
+        for lines in drain_insert_history(&mut rx) {
+            crate::insert_history::insert_history_lines(&mut terminal, lines)
+                .expect("insert history lines");
+        }
+
+        terminal
+            .draw(|frame| chat.render(frame.area(), frame.buffer_mut()))
+            .expect("draw final answer");
+        assert_chatwidget_snapshot!(
+            snapshot,
+            normalize_snapshot_paths(terminal.backend().vt100().screen().contents())
+        );
     }
-
-    terminal
-        .draw(|frame| chat.render(frame.area(), frame.buffer_mut()))
-        .expect("draw final answer");
-    assert_chatwidget_snapshot!(
-        "single_line_final_answer_hides_working_status",
-        normalize_snapshot_paths(terminal.backend().vt100().screen().contents())
-    );
 }
 
 #[tokio::test]

sdk/python/src/openai_codex/generated/v2_all.py

@@ -2750,6 +2750,7 @@ class MergeStrategy(Enum):
 
 class MessagePhase(Enum):
     commentary = "commentary"
+    partial_answer = "partial_answer"
     final_answer = "final_answer"