diff --git a/packages/client/ui-subagent/src/client/SubagentHeaderLineage.tsx b/packages/client/ui-subagent/src/client/SubagentHeaderLineage.tsx
index e528cde037..f3885f26c4 100644
--- a/packages/client/ui-subagent/src/client/SubagentHeaderLineage.tsx
+++ b/packages/client/ui-subagent/src/client/SubagentHeaderLineage.tsx
@@ -296,7 +296,6 @@ function CatalogRows({
         const openAside = (event: MouseEvent<HTMLButtonElement>): void => {
           event.preventDefault()
           event.stopPropagation()
-          if (external) return
           openChildAside({ parentSessionId, childSessionId: entry.id, mode: entry.mode })
           closeCatalog()
         }
diff --git a/scripts/snapshots/python-sdk-single-exe/advanced/result.json b/scripts/snapshots/python-sdk-single-exe/advanced/result.json
index 30d9d06ae1..bb91f56f08 100644
--- a/scripts/snapshots/python-sdk-single-exe/advanced/result.json
+++ b/scripts/snapshots/python-sdk-single-exe/advanced/result.json
@@ -1362,21 +1362,9 @@
         "name": "advanced-exe-snapshot"
       }
     },
-    {
-      "type": "subagent/catalog",
-      "seq": 54,
-      "time": 0,
-      "data": {
-        "version": 0,
-        "childId": "{{child-2}}",
-        "childCreatedAt": 0,
-        "mode": "continuable",
-        "label": "advanced-exe-snapshot child 1"
-      }
-    },
     {
       "type": "tool-workflow/agent-start",
-      "seq": 55,
+      "seq": 54,
       "time": 0,
       "data": {
         "runId": "{{workflow-run}}",
@@ -1388,7 +1376,7 @@
     },
     {
       "type": "tool-workflow/agent-end",
-      "seq": 56,
+      "seq": 55,
       "time": 0,
       "data": {
         "runId": "{{workflow-run}}",
@@ -1398,7 +1386,7 @@
     },
     {
       "type": "tool-workflow/run-end",
-      "seq": 57,
+      "seq": 56,
       "time": 0,
       "data": {
         "runId": "{{workflow-run}}",
@@ -1407,7 +1395,7 @@
     },
     {
       "type": "tool/result",
-      "seq": 58,
+      "seq": 57,
       "time": 0,
       "data": {
         "turn": 1,
@@ -1436,7 +1424,7 @@
     },
     {
       "type": "step/end",
-      "seq": 59,
+      "seq": 58,
       "time": 0,
       "data": {
         "turn": 1,
@@ -1445,7 +1433,7 @@
     },
     {
       "type": "agent/inbox/spliced",
-      "seq": 60,
+      "seq": 59,
       "time": 0,
       "data": {
         "target": "next-step",
@@ -1456,7 +1444,7 @@
     },
     {
       "type": "step/start",
-      "seq": 61,
+      "seq": 60,
       "time": 0,
       "data": {
         "turn": 1,
@@ -1465,7 +1453,7 @@
     },
     {
       "type": "user/message",
-      "seq": 62,
+      "seq": 61,
       "time": 0,
       "data": {
         "content": [
@@ -1495,17 +1483,17 @@
     },
     {
       "type": "session-log-deepseek/delivery-accepted",
-      "seq": 63,
+      "seq": 62,
       "time": 0,
       "data": {
         "sessionId": "{{parent}}",
         "sessionFormatVersion": 4,
-        "throughSeq": 62
+        "throughSeq": 61
       }
     },
     {
       "type": "assistant/message",
-      "seq": 64,
+      "seq": 63,
       "time": 0,
       "data": {
         "turn": 1,
@@ -1613,7 +1601,7 @@
     },
     {
       "type": "step/end",
-      "seq": 65,
+      "seq": 64,
       "time": 0,
       "data": {
         "turn": 1,
@@ -1622,7 +1610,7 @@
     },
     {
       "type": "command/run",
-      "seq": 66,
+      "seq": 65,
       "time": 0,
       "data": {
         "commandId": "{{command:1}}",
@@ -1634,7 +1622,7 @@
     },
     {
       "type": "feedback/record",
-      "seq": 67,
+      "seq": 66,
       "time": 0,
       "data": {
         "text": "The session needs a clearer explanation."
@@ -1642,7 +1630,7 @@
     },
     {
       "type": "command/done",
-      "seq": 68,
+      "seq": 67,
       "time": 0,
       "data": {
         "commandId": "{{command:1}}",
@@ -1652,7 +1640,7 @@
     },
     {
       "type": "feedback/record",
-      "seq": 69,
+      "seq": 68,
       "time": 0,
       "data": {
         "category": "other"
@@ -1660,7 +1648,7 @@
     },
     {
       "type": "feedback/message-put",
-      "seq": 70,
+      "seq": 69,
       "time": 0,
       "data": {
         "sessionId": "{{parent}}",
@@ -1677,7 +1665,7 @@
     },
     {
       "type": "feedback/message-put",
-      "seq": 71,
+      "seq": 70,
       "time": 0,
       "data": {
         "sessionId": "{{parent}}",
@@ -1693,7 +1681,7 @@
     },
     {
       "type": "feedback/message-delete",
-      "seq": 72,
+      "seq": 71,
       "time": 0,
       "data": {
         "sessionId": "{{parent}}",
@@ -1702,7 +1690,7 @@
     },
     {
       "type": "turn/end",
-      "seq": 73,
+      "seq": 72,
       "time": 0,
       "data": {
         "turn": 1,
@@ -4016,31 +4004,13 @@
         }
       }
     },
-    {
-      "method": "session.event",
-      "payload": {
-        "sessionId": "{{parent}}",
-        "event": {
-          "type": "subagent/catalog",
-          "seq": 54,
-          "time": 0,
-          "data": {
-            "version": 0,
-            "childId": "{{child-2}}",
-            "childCreatedAt": 0,
-            "mode": "continuable",
-            "label": "advanced-exe-snapshot child 1"
-          }
-        }
-      }
-    },
     {
       "method": "session.event",
       "payload": {
         "sessionId": "{{parent}}",
         "event": {
           "type": "tool-workflow/agent-start",
-          "seq": 55,
+          "seq": 54,
           "time": 0,
           "data": {
             "runId": "{{workflow-run}}",
@@ -4450,7 +4420,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "tool-workflow/agent-end",
-          "seq": 56,
+          "seq": 55,
           "time": 0,
           "data": {
             "runId": "{{workflow-run}}",
@@ -4466,7 +4436,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "tool-workflow/run-end",
-          "seq": 57,
+          "seq": 56,
           "time": 0,
           "data": {
             "runId": "{{workflow-run}}",
@@ -4481,7 +4451,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "tool/result",
-          "seq": 58,
+          "seq": 57,
           "time": 0,
           "data": {
             "turn": 1,
@@ -4516,7 +4486,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "step/end",
-          "seq": 59,
+          "seq": 58,
           "time": 0,
           "data": {
             "turn": 1,
@@ -4531,7 +4501,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "agent/inbox/spliced",
-          "seq": 60,
+          "seq": 59,
           "time": 0,
           "data": {
             "target": "next-step",
@@ -4548,7 +4518,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "step/start",
-          "seq": 61,
+          "seq": 60,
           "time": 0,
           "data": {
             "turn": 1,
@@ -4563,7 +4533,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "user/message",
-          "seq": 62,
+          "seq": 61,
           "time": 0,
           "data": {
             "content": [
@@ -4599,12 +4569,12 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "session-log-deepseek/delivery-accepted",
-          "seq": 63,
+          "seq": 62,
           "time": 0,
           "data": {
             "sessionId": "{{parent}}",
             "sessionFormatVersion": 4,
-            "throughSeq": 62
+            "throughSeq": 61
           }
         }
       }
@@ -4615,7 +4585,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "assistant/message",
-          "seq": 64,
+          "seq": 63,
           "time": 0,
           "data": {
             "turn": 1,
@@ -4729,7 +4699,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "step/end",
-          "seq": 65,
+          "seq": 64,
           "time": 0,
           "data": {
             "turn": 1,
@@ -4744,7 +4714,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "command/run",
-          "seq": 66,
+          "seq": 65,
           "time": 0,
           "data": {
             "commandId": "{{command:1}}",
@@ -4762,7 +4732,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "feedback/record",
-          "seq": 67,
+          "seq": 66,
           "time": 0,
           "data": {
             "text": "The session needs a clearer explanation."
@@ -4776,7 +4746,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "command/done",
-          "seq": 68,
+          "seq": 67,
           "time": 0,
           "data": {
             "commandId": "{{command:1}}",
@@ -4792,7 +4762,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "feedback/record",
-          "seq": 69,
+          "seq": 68,
           "time": 0,
           "data": {
             "category": "other"
@@ -4806,7 +4776,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "feedback/message-put",
-          "seq": 70,
+          "seq": 69,
           "time": 0,
           "data": {
             "sessionId": "{{parent}}",
@@ -4829,7 +4799,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "feedback/message-put",
-          "seq": 71,
+          "seq": 70,
           "time": 0,
           "data": {
             "sessionId": "{{parent}}",
@@ -4851,7 +4821,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "feedback/message-delete",
-          "seq": 72,
+          "seq": 71,
           "time": 0,
           "data": {
             "sessionId": "{{parent}}",
@@ -4866,7 +4836,7 @@
         "sessionId": "{{parent}}",
         "event": {
           "type": "turn/end",
-          "seq": 73,
+          "seq": 72,
           "time": 0,
           "data": {
             "turn": 1,
diff --git a/scripts/snapshots/python-sdk-single-exe/advanced/session.v4.jsonl b/scripts/snapshots/python-sdk-single-exe/advanced/session.v4.jsonl
index 329c9868d2..19681dbe0a 100644
--- a/scripts/snapshots/python-sdk-single-exe/advanced/session.v4.jsonl
+++ b/scripts/snapshots/python-sdk-single-exe/advanced/session.v4.jsonl
@@ -53,7 +53,6 @@
 {"type":"assistant/message","data":{"turn":1,"step":5,"message":{"role":"assistant","content":[{"type":"tool-call","id":"advanced-workflow","name":"workflow","arguments":"{\"script\": \"phase('Delegate')\\nconst reply = await agent('Reply with exactly WORKFLOW_CHILD_OK and nothing else.', { label: 'workflow-child' })\\nreturn { reply }\", \"meta\": {\"name\": \"advanced-exe-snapshot\", \"description\": \"exercise one packaged workflow child\"}}"}],"source":{"kind":"model","provider":"deepseek-official","model":"smoke-model","replayState":{"response":{"kind":"deepseek-messages","version":1,"model":"smoke-model"},"blocks":[{"type":"tool-call"}]}},"id":"{{messageId}}"},"usage":{"inputTokens":3,"outputTokens":3,"totalTokens":6},"stream":[{"type":"chunk","time":0,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}},{"type":"tool-call-chunks","time0":0,"index":0,"dt":[],"id":"advanced-workflow","name":"workflow","args":[""]},{"type":"tool-call-chunks","time0":0,"index":0,"dt":[],"id":"advanced-workflow","args":["{\"script\": \"phase('Delegate')\\nconst reply = await agent('Reply with exactly WORKFLOW_CHILD_OK and nothing else.', { label: 'workflow-child' })\\nreturn { reply }\", \"meta\": {\"name\": \"advanced-exe-snapshot\", \"description\": \"exercise one packaged workflow child\"}}"]},{"type":"chunk","time":0,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"advanced-workflow","name":"workflow","arguments":"{\"script\": \"phase('Delegate')\\nconst reply = await agent('Reply with exactly WORKFLOW_CHILD_OK and nothing else.', { label: 'workflow-child' })\\nreturn { reply }\", \"meta\": {\"name\": \"advanced-exe-snapshot\", \"description\": \"exercise one packaged workflow child\"}}"}}},{"type":"chunk","time":0,"chunk":{"type":"usage","usage":{"inputTokens":3,"outputTokens":3,"totalTokens":6}}},{"type":"chunk","time":0,"chunk":{"type":"finish","reason":{"kind":"tool-calls"},"replayState":{"response":{"kind":"deepseek-messages","version":1,"model":"smoke-model"},"blocks":[{"type":"tool-call"}]}}}]},"surfaceOp":"append"}
 {"type":"tool/call","data":{"turn":1,"step":5,"callId":"advanced-workflow","name":"workflow","arguments":"{\"script\": \"phase('Delegate')\\nconst reply = await agent('Reply with exactly WORKFLOW_CHILD_OK and nothing else.', { label: 'workflow-child' })\\nreturn { reply }\", \"meta\": {\"name\": \"advanced-exe-snapshot\", \"description\": \"exercise one packaged workflow child\"}}"}}
 {"type":"tool-workflow/run-start","data":{"runId":"{{workflow-run}}","name":"advanced-exe-snapshot"}}
-{"type":"subagent/catalog","data":{"version":0,"childId":"{{child-2}}","childCreatedAt":0,"mode":"continuable","label":"advanced-exe-snapshot child 1"}}
 {"type":"tool-workflow/agent-start","data":{"runId":"{{workflow-run}}","seq":1,"label":"workflow-child","phase":"Delegate","childId":"{{child-2}}"}}
 {"type":"tool-workflow/agent-end","data":{"runId":"{{workflow-run}}","seq":1,"outcome":"completed"}}
 {"type":"tool-workflow/run-end","data":{"runId":"{{workflow-run}}","stopReason":"completed"}}
@@ -62,7 +61,7 @@
 {"type":"agent/inbox/spliced","data":{"target":"next-step","start":0,"removedCount":1,"inserted":[]}}
 {"type":"step/start","data":{"turn":1,"step":6}}
 {"type":"user/message","data":{"content":[{"type":"text","text":"Background subagent {{child-1}} finished and will do no further work unless you send it more."},{"type":"text","text":"Its closing message:"},{"type":"text","text":"DIRECT_CHILD_OK"}],"source":{"kind":"subagent-settled","form":"notice","summary":"Background subagent {{child-1}} finished and will do no further work unless you send it more.","senderSessionId":"{{child-1}}"},"role":"user","id":"{{messageId}}"},"surfaceOp":"append"}
-{"type":"session-log-deepseek/delivery-accepted","data":{"sessionId":"{{parent}}","sessionFormatVersion":4,"throughSeq":62}}
+{"type":"session-log-deepseek/delivery-accepted","data":{"sessionId":"{{parent}}","sessionFormatVersion":4,"throughSeq":61}}
 {"type":"assistant/message","data":{"turn":1,"step":6,"message":{"role":"assistant","content":[{"type":"text","text":"ADVANCED_EXECUTABLE_OK"}],"source":{"kind":"model","provider":"deepseek-official","model":"smoke-model","replayState":{"response":{"kind":"deepseek-messages","version":1,"model":"smoke-model"},"blocks":[{"type":"text"}]}},"id":"{{message:1}}"},"usage":{"inputTokens":3,"outputTokens":3,"totalTokens":6},"stream":[{"type":"chunk","time":0,"chunk":{"type":"block-start","index":0,"blockType":"text"}},{"type":"text-chunks","time0":0,"index":0,"dt":[],"texts":["ADVANCED_EXECUTABLE_OK"]},{"type":"chunk","time":0,"chunk":{"type":"block-end","index":0,"block":{"type":"text","text":"ADVANCED_EXECUTABLE_OK"}}},{"type":"chunk","time":0,"chunk":{"type":"usage","usage":{"inputTokens":3,"outputTokens":3,"totalTokens":6}}},{"type":"chunk","time":0,"chunk":{"type":"finish","reason":{"kind":"stop"},"replayState":{"response":{"kind":"deepseek-messages","version":1,"model":"smoke-model"},"blocks":[{"type":"text"}]}}}]},"surfaceOp":"append"}
 {"type":"step/end","data":{"turn":1,"step":6}}
 {"type":"command/run","data":{"commandId":"{{command:1}}","name":"feedback","source":{"kind":"user"}}}
diff --git a/snapshots/session/persistent-pwsh-tool-turn/session.v4.jsonl b/snapshots/session/persistent-pwsh-tool-turn/session.v4.jsonl
new file mode 100644
index 0000000000..a7337c979b
--- /dev/null
+++ b/snapshots/session/persistent-pwsh-tool-turn/session.v4.jsonl
@@ -0,0 +1,22 @@
+{"type":"session","version":4,"id":"{{session:1}}","createdAt":0,"cwd":"{{cwd}}","isSeeded":false,"delegationDepth":0}
+{"type":"permission/preset","data":{"preset":"danger-full-access"}}
+{"type":"sandbox/mode","data":{"mode":"danger-full-access"}}
+{"type":"approval/policy","data":{"policy":"never"}}
+{"type":"agent/inbox/spliced","data":{"target":"next-turn","start":0,"inserted":[{"content":[{"type":"text","text":"Use the pwsh tool to run exactly: [Console]::Out.Write('PWSH_OK'). Then reply with the single word DONE and stop."}],"source":{"kind":"user"},"role":"user","id":"{{message:1}}"}]}}
+{"type":"turn/start","data":{"turn":1}}
+{"type":"agent/inbox/spliced","data":{"target":"next-turn","start":0,"removedCount":1,"inserted":[]}}
+{"type":"step/start","data":{"turn":1,"step":1}}
+{"type":"system/message","data":{"turn":1,"step":1,"message":{"role":"system","content":[{"type":"text","text":"{{system}}"}],"source":{"kind":"system-prompt"},"id":"{{message:2}}"}},"surfaceOp":"append"}
+{"type":"user/message","data":{"content":[{"type":"text","text":"Use the pwsh tool to run exactly: [Console]::Out.Write('PWSH_OK'). Then reply with the single word DONE and stop."}],"source":{"kind":"user"},"role":"user","id":"{{message:1}}"},"surfaceOp":"append"}
+{"type":"user/message","data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."}],"source":{"kind":"runtime-context","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."}]},"role":"user","id":"{{message:3}}"},"surfaceOp":"append"}
+{"type":"request/header","data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-pro"},"tools":"{{tools}}"},"reason":"initial"}}
+{"type":"request/context","data":{"provider":"deepseek-official","model":"deepseek-v4-pro"}}
+{"type":"session/title","data":{"title":"Use the pwsh tool to","messageSeqs":[8],"source":{"kind":"fallback"}}}
+{"type":"assistant/message","data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user wants me to run a PowerShell command and then reply with \"DONE\". Let me execute it."},{"type":"tool-call","id":"call_00_e0MSVSocL0o4UWjOdG4c2072","name":"pwsh","arguments":"{\"command\":\"[Console]::Out.Write('PWSH_OK')\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-pro"},"id":"{{message:4}}"},"usage":{"inputTokens":1255,"outputTokens":99,"cacheReadTokens":0,"reasoningTokens":22},"stream":[{"type":"chunk","time":1788699792646,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}},{"type":"reasoning-chunks","time0":1788699792647,"index":0,"dt":[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],"texts":["The"," user"," wants"," me"," to"," run"," a"," PowerShell"," command"," and"," then"," reply"," with"," \"","D","ONE","\"."," Let"," me"," execute"," it","."]},{"type":"chunk","time":1788699792647,"chunk":{"type":"block-start","index":1,"blockType":"tool-call"}},{"type":"tool-call-chunks","time0":1788699792647,"index":1,"dt":[0,0,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0],"id":"call_00_e0MSVSocL0o4UWjOdG4c2072","name":"pwsh","args":["","{","\"","command","\"",": ","\"","[","Console","]","::","Out",".Write","('","P","WS","H","_OK","')","\"","}"]},{"type":"chunk","time":1788699792648,"chunk":{"type":"block-end","index":0,"block":{"type":"reasoning","text":"The user wants me to run a PowerShell command and then reply with \"DONE\". Let me execute it."}}},{"type":"chunk","time":1788699792648,"chunk":{"type":"block-end","index":1,"block":{"type":"tool-call","id":"call_00_e0MSVSocL0o4UWjOdG4c2072","name":"pwsh","arguments":"{\"command\":\"[Console]::Out.Write('PWSH_OK')\"}"}}},{"type":"chunk","time":1788699792648,"chunk":{"type":"usage","usage":{"inputTokens":1255,"outputTokens":99,"cacheReadTokens":0,"reasoningTokens":22}}},{"type":"chunk","time":1788699792648,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}]},"surfaceOp":"append"}
+{"type":"tool/call","data":{"turn":1,"step":1,"callId":"call_00_e0MSVSocL0o4UWjOdG4c2072","name":"pwsh","arguments":"{\"command\":\"[Console]::Out.Write('PWSH_OK')\"}"}}
+{"type":"tool/result","data":{"turn":1,"step":1,"message":{"role":"tool","source":{"kind":"tool","callId":"call_00_e0MSVSocL0o4UWjOdG4c2072"},"toolCallId":"call_00_e0MSVSocL0o4UWjOdG4c2072","content":[{"type":"text","text":"PWSH_OK"}],"isError":false,"id":"{{message:5}}"}},"sourceEventSeqs":[14],"surfaceOp":"append"}
+{"type":"step/end","data":{"turn":1,"step":1}}
+{"type":"step/start","data":{"turn":1,"step":2}}
+{"type":"assistant/message","data":{"turn":1,"step":2,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The command executed successfully and printed \"PWSH_OK\". Now I need to reply with \"DONE\" and stop."},{"type":"text","text":"DONE"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-pro"},"id":"{{message:6}}"},"usage":{"inputTokens":90,"outputTokens":28,"cacheReadTokens":1280,"reasoningTokens":25},"stream":[{"type":"chunk","time":1788699806478,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}},{"type":"reasoning-chunks","time0":1788699806478,"index":0,"dt":[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],"texts":["The"," command"," executed"," successfully"," and"," printed"," \"","P","WS","H","_OK","\"."," Now"," I"," need"," to"," reply"," with"," \"","D","ONE","\""," and"," stop","."]},{"type":"chunk","time":1788699806478,"chunk":{"type":"block-start","index":1,"blockType":"text"}},{"type":"text-chunks","time0":1788699806478,"index":1,"dt":[0],"texts":["D","ONE"]},{"type":"chunk","time":1788699806478,"chunk":{"type":"block-end","index":0,"block":{"type":"reasoning","text":"The command executed successfully and printed \"PWSH_OK\". Now I need to reply with \"DONE\" and stop."}}},{"type":"chunk","time":1788699806478,"chunk":{"type":"block-end","index":1,"block":{"type":"text","text":"DONE"}}},{"type":"chunk","time":1788699806478,"chunk":{"type":"usage","usage":{"inputTokens":90,"outputTokens":28,"cacheReadTokens":1280,"reasoningTokens":25}}},{"type":"chunk","time":1788699806478,"chunk":{"type":"finish","reason":{"kind":"stop"}}}]},"surfaceOp":"append"}
+{"type":"step/end","data":{"turn":1,"step":2}}
+{"type":"turn/end","data":{"turn":1,"reason":{"kind":"completed"}}}
diff --git a/snapshots/session/persistent-pwsh-tool-turn/tool-schemas.expected.json b/snapshots/session/persistent-pwsh-tool-turn/tool-schemas.expected.json
index 399231d0db..037274da5c 100644
--- a/snapshots/session/persistent-pwsh-tool-turn/tool-schemas.expected.json
+++ b/snapshots/session/persistent-pwsh-tool-turn/tool-schemas.expected.json
@@ -214,7 +214,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool starts an independently managed subagent and immediately returns its id. The runtime notifies you when it finishes. The child reports results with `send_message`; use `send_message` to steer it while running or continue its conversation after it finishes.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. This tool starts an independently managed subagent and immediately returns its id. The runtime notifies you when it finishes. The child reports results with `send_message`; use `send_message` to steer it while running or continue its conversation after it finishes.",
       "parameters": {
         "type": "object",
         "properties": {
diff --git a/snapshots/session/pwsh-tool-turn/session.v4.jsonl b/snapshots/session/pwsh-tool-turn/session.v4.jsonl
new file mode 100644
index 0000000000..e00924d0cd
--- /dev/null
+++ b/snapshots/session/pwsh-tool-turn/session.v4.jsonl
@@ -0,0 +1,22 @@
+{"type":"session","version":4,"id":"{{session:1}}","createdAt":0,"cwd":"{{cwd}}","isSeeded":false,"delegationDepth":0}
+{"type":"permission/preset","data":{"preset":"danger-full-access"}}
+{"type":"sandbox/mode","data":{"mode":"danger-full-access"}}
+{"type":"approval/policy","data":{"policy":"never"}}
+{"type":"agent/inbox/spliced","data":{"target":"next-turn","start":0,"inserted":[{"content":[{"type":"text","text":"Use the pwsh tool to run exactly: [Console]::Out.Write('PWSH_OK'). Then reply with the single word DONE and stop."}],"source":{"kind":"user"},"role":"user","id":"{{message:1}}"}]}}
+{"type":"turn/start","data":{"turn":1}}
+{"type":"agent/inbox/spliced","data":{"target":"next-turn","start":0,"removedCount":1,"inserted":[]}}
+{"type":"step/start","data":{"turn":1,"step":1}}
+{"type":"system/message","data":{"turn":1,"step":1,"message":{"role":"system","content":[{"type":"text","text":"{{system}}"}],"source":{"kind":"system-prompt"},"id":"{{message:2}}"}},"surfaceOp":"append"}
+{"type":"user/message","data":{"content":[{"type":"text","text":"Use the pwsh tool to run exactly: [Console]::Out.Write('PWSH_OK'). Then reply with the single word DONE and stop."}],"source":{"kind":"user"},"role":"user","id":"{{message:1}}"},"surfaceOp":"append"}
+{"type":"user/message","data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."}],"source":{"kind":"runtime-context","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."}]},"role":"user","id":"{{message:3}}"},"surfaceOp":"append"}
+{"type":"request/header","data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-pro"},"tools":"{{tools}}"},"reason":"initial"}}
+{"type":"request/context","data":{"provider":"deepseek-official","model":"deepseek-v4-pro"}}
+{"type":"session/title","data":{"title":"Use the pwsh tool to","messageSeqs":[8],"source":{"kind":"fallback"}}}
+{"type":"assistant/message","data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user wants me to run a PowerShell command and then reply with \"DONE\". Let me execute it."},{"type":"tool-call","id":"call_00_e0MSVSocL0o4UWjOdG4c2072","name":"pwsh","arguments":"{\"command\": \"[Console]::Out.Write('PWSH_OK')\", \"description\": \"Write PWSH_OK to console\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-pro"},"id":"{{message:4}}"},"usage":{"inputTokens":1255,"outputTokens":99,"cacheReadTokens":0,"reasoningTokens":22},"stream":[{"type":"chunk","time":1788699810924,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}},{"type":"reasoning-chunks","time0":1788699810924,"index":0,"dt":[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1],"texts":["The"," user"," wants"," me"," to"," run"," a"," PowerShell"," command"," and"," then"," reply"," with"," \"","D","ONE","\"."," Let"," me"," execute"," it","."]},{"type":"chunk","time":1788699810925,"chunk":{"type":"block-start","index":1,"blockType":"tool-call"}},{"type":"tool-call-chunks","time0":1788699810925,"index":1,"dt":[0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],"id":"call_00_e0MSVSocL0o4UWjOdG4c2072","name":"pwsh","args":["","{","\"","command","\"",": ","\"","[","Console","]","::","Out",".Write","('","P","WS","H","_OK","')","\"",", ","\"","description","\"",": ","\"","Write"," P","WS","H","_OK"," to"," console","\"","}"]},{"type":"chunk","time":1788699810925,"chunk":{"type":"block-end","index":0,"block":{"type":"reasoning","text":"The user wants me to run a PowerShell command and then reply with \"DONE\". Let me execute it."}}},{"type":"chunk","time":1788699810925,"chunk":{"type":"block-end","index":1,"block":{"type":"tool-call","id":"call_00_e0MSVSocL0o4UWjOdG4c2072","name":"pwsh","arguments":"{\"command\": \"[Console]::Out.Write('PWSH_OK')\", \"description\": \"Write PWSH_OK to console\"}"}}},{"type":"chunk","time":1788699810925,"chunk":{"type":"usage","usage":{"inputTokens":1255,"outputTokens":99,"cacheReadTokens":0,"reasoningTokens":22}}},{"type":"chunk","time":1788699810925,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}]},"surfaceOp":"append"}
+{"type":"tool/call","data":{"turn":1,"step":1,"callId":"call_00_e0MSVSocL0o4UWjOdG4c2072","name":"pwsh","arguments":"{\"command\": \"[Console]::Out.Write('PWSH_OK')\", \"description\": \"Write PWSH_OK to console\"}"}}
+{"type":"tool/result","data":{"turn":1,"step":1,"message":{"role":"tool","source":{"kind":"tool","callId":"call_00_e0MSVSocL0o4UWjOdG4c2072"},"toolCallId":"call_00_e0MSVSocL0o4UWjOdG4c2072","content":[{"type":"text","text":"PWSH_OK"}],"isError":false,"id":"{{message:5}}"}},"sourceEventSeqs":[14],"surfaceOp":"append"}
+{"type":"step/end","data":{"turn":1,"step":1}}
+{"type":"step/start","data":{"turn":1,"step":2}}
+{"type":"assistant/message","data":{"turn":1,"step":2,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The command executed successfully and printed \"PWSH_OK\". Now I need to reply with \"DONE\" and stop."},{"type":"text","text":"DONE"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-pro"},"id":"{{message:6}}"},"usage":{"inputTokens":90,"outputTokens":28,"cacheReadTokens":1280,"reasoningTokens":25},"stream":[{"type":"chunk","time":1788699811198,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}},{"type":"reasoning-chunks","time0":1788699811198,"index":0,"dt":[1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0],"texts":["The"," command"," executed"," successfully"," and"," printed"," \"","P","WS","H","_OK","\"."," Now"," I"," need"," to"," reply"," with"," \"","D","ONE","\""," and"," stop","."]},{"type":"chunk","time":1788699811199,"chunk":{"type":"block-start","index":1,"blockType":"text"}},{"type":"text-chunks","time0":1788699811199,"index":1,"dt":[0],"texts":["D","ONE"]},{"type":"chunk","time":1788699811199,"chunk":{"type":"block-end","index":0,"block":{"type":"reasoning","text":"The command executed successfully and printed \"PWSH_OK\". Now I need to reply with \"DONE\" and stop."}}},{"type":"chunk","time":1788699811199,"chunk":{"type":"block-end","index":1,"block":{"type":"text","text":"DONE"}}},{"type":"chunk","time":1788699811199,"chunk":{"type":"usage","usage":{"inputTokens":90,"outputTokens":28,"cacheReadTokens":1280,"reasoningTokens":25}}},{"type":"chunk","time":1788699811199,"chunk":{"type":"finish","reason":{"kind":"stop"}}}]},"surfaceOp":"append"}
+{"type":"step/end","data":{"turn":1,"step":2}}
+{"type":"turn/end","data":{"turn":1,"reason":{"kind":"completed"}}}
diff --git a/snapshots/session/pwsh-tool-turn/tool-schemas.expected.json b/snapshots/session/pwsh-tool-turn/tool-schemas.expected.json
index 4c6506aef0..24365c5bd1 100644
--- a/snapshots/session/pwsh-tool-turn/tool-schemas.expected.json
+++ b/snapshots/session/pwsh-tool-turn/tool-schemas.expected.json
@@ -295,7 +295,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool starts an independently managed subagent and immediately returns its id. The runtime notifies you when it finishes. The child reports results with `send_message`; use `send_message` to steer it while running or continue its conversation after it finishes.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. This tool starts an independently managed subagent and immediately returns its id. The runtime notifies you when it finishes. The child reports results with `send_message`; use `send_message` to steer it while running or continue its conversation after it finishes.",
       "parameters": {
         "type": "object",
         "properties": {
diff --git a/snapshots/web/diff-context/snapshot.yml b/snapshots/web/diff-context/snapshot.yml
index bbf913c8e1..a873709b05 100644
--- a/snapshots/web/diff-context/snapshot.yml
+++ b/snapshots/web/diff-context/snapshot.yml
@@ -6,4 +6,4 @@ recording: authored
 header:
   class: default
 session:
-  source: ../../session/fs-edit/session.v3.jsonl
+  source: ../../session/fs-edit/session.v4.jsonl
diff --git a/snapshots/web/fresh-round-trip/tool-schemas.expected.json b/snapshots/web/fresh-round-trip/tool-schemas.expected.json
index 041de08209..5e734ea78d 100644
--- a/snapshots/web/fresh-round-trip/tool-schemas.expected.json
+++ b/snapshots/web/fresh-round-trip/tool-schemas.expected.json
@@ -435,7 +435,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool starts an independently managed subagent and immediately returns its id. The runtime notifies you when it finishes. The child reports results with `send_message`; use `send_message` to steer it while running or continue its conversation after it finishes.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. This tool starts an independently managed subagent and immediately returns its id. The runtime notifies you when it finishes. The child reports results with `send_message`; use `send_message` to steer it while running or continue its conversation after it finishes.",
       "parameters": {
         "type": "object",
         "properties": {
diff --git a/snapshots/web/ptc-round/system-prompt.expected.md b/snapshots/web/ptc-round/system-prompt.expected.md
index 01914968aa..b1552405ba 100644
--- a/snapshots/web/ptc-round/system-prompt.expected.md
+++ b/snapshots/web/ptc-round/system-prompt.expected.md
@@ -130,7 +130,7 @@ interface ToolArgsMap {
     /** One glob filter for which files to search (e.g. "*.ts", "*.{js,jsx}"). Not a list; negation is not supported. */
     include?: string;
   } & Record<string, JsonValue>;
-  /** Request cancellation of a background agent's current turn by its agent id. The target may be your direct child or a deeper agent created under you. For local agents, only the current turn stops: messages already queued for the agent stay parked until a later send_message, agents it started keep running, and the agent itself stays available for follow-ups. External executions stop permanently and cannot receive follow-ups. This call returns as soon as the stop request is accepted, so the target may keep running briefly; interrupting an agent that already finished is an accepted no-op. */
+  /** Ask a subagent to stop its current work. This call returns without waiting for it to stop. You can continue a local direct child's conversation later with send_message. External executions stop permanently and cannot receive follow-ups. Subagents it started will keep running. */
   interrupt_agent: {
     /** The id of an agent created under you: your direct child or a deeper descendant. */
     agent_id: string;
@@ -194,7 +194,7 @@ interface ToolArgsMap {
     /** The exact skill name from the available skills list. */
     name: string;
   } & Record<string, JsonValue>;
-  /** Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool starts an independently managed subagent and immediately returns its id. The runtime notifies you when it finishes. The child reports results with `send_message`; use `send_message` to steer it while running or continue its conversation after it finishes. */
+  /** Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. This tool starts an independently managed subagent and immediately returns its id. The runtime notifies you when it finishes. The child reports results with `send_message`; use `send_message` to steer it while running or continue its conversation after it finishes. */
   subagent: {
     /** A short (3-5 word) description of the delegated task, for display. */
     description: string;