Fix fork source display in /status (expose forked_from_id in app server) (#16596)

Addresses #16560

Problem: `/status` stopped showing the source thread id in forked TUI
sessions after the app-server migration.

Solution: Carry fork source ids through app-server v2 thread data and
the TUI session adapter, and update TUI fixtures so `/status` matches
the old TUI behavior.

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

@@ -2425,6 +2425,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -12186,6 +12186,13 @@
             "description": "Whether the thread is ephemeral and should not be materialized on disk.",
             "type": "boolean"
           },
+          "forkedFromId": {
+            "description": "Source thread id when this thread was created by forking another thread.",
+            "type": [
+              "string",
+              "null"
+            ]
+          },
           "gitInfo": {
             "anyOf": [
               {

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

@@ -10041,6 +10041,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -1042,6 +1042,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -800,6 +800,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -800,6 +800,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -800,6 +800,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -1042,6 +1042,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -800,6 +800,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -1042,6 +1042,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -800,6 +800,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

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

@@ -800,6 +800,13 @@
           "description": "Whether the thread is ephemeral and should not be materialized on disk.",
           "type": "boolean"
         },
+        "forkedFromId": {
+          "description": "Source thread id when this thread was created by forking another thread.",
+          "type": [
+            "string",
+            "null"
+          ]
+        },
         "gitInfo": {
           "anyOf": [
             {

codex-rs/app-server-protocol/schema/typescript/v2/Thread.ts

@@ -7,6 +7,10 @@ import type { ThreadStatus } from "./ThreadStatus";
 import type { Turn } from "./Turn";
 
 export type Thread = { id: string, 
+/**
+ * Source thread id when this thread was created by forking another thread.
+ */
+forkedFromId: string | null, 
 /**
  * Usually the first user message in the thread, if available.
  */

codex-rs/app-server-protocol/src/protocol/common.rs

@@ -1307,6 +1307,7 @@ mod tests {
             response: v2::ThreadStartResponse {
                 thread: v2::Thread {
                     id: "67e55044-10b1-426f-9247-bb680e5fe0c8".to_string(),
+                    forked_from_id: None,
                     preview: "first prompt".to_string(),
                     ephemeral: true,
                     model_provider: "openai".to_string(),
@@ -1343,6 +1344,7 @@ mod tests {
                 "response": {
                     "thread": {
                         "id": "67e55044-10b1-426f-9247-bb680e5fe0c8",
+                        "forkedFromId": null,
                         "preview": "first prompt",
                         "ephemeral": true,
                         "modelProvider": "openai",

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -3574,6 +3574,8 @@ impl From<CoreSkillErrorInfo> for SkillErrorInfo {
 #[ts(export_to = "v2/")]
 pub struct Thread {
     pub id: String,
+    /// Source thread id when this thread was created by forking another thread.
+    pub forked_from_id: Option<String>,
     /// Usually the first user message in the thread, if available.
     pub preview: String,
     /// Whether the thread is ephemeral and should not be materialized on disk.