fix(session): make ordinary forks independent of source lineage

scripts/snapshots/python-sdk-single-exe/advanced-ptc/result.json

@@ -98,7 +98,7 @@
         "content": [
           {
             "type": "text",
-            "text": "Serial agent creation completed."
+            "text": "Serial agent creation completed. Ordinary and nested forks are independent; historical fork metadata remains readable."
           }
         ],
         "source": {
@@ -1156,7 +1156,7 @@
             "content": [
               {
                 "type": "text",
-                "text": "Serial agent creation completed."
+                "text": "Serial agent creation completed. Ordinary and nested forks are independent; historical fork metadata remains readable."
               }
             ],
             "source": {

scripts/snapshots/python-sdk-single-exe/advanced-ptc/session.v4.jsonl

@@ -2,14 +2,14 @@
 {"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-step","start":0,"inserted":[{"id":"{{messageId}}","role":"user","content":[{"type":"text","text":"Serial agent creation completed."}],"source":{"kind":"plugin:serial-created-fixture"}}]}}
+{"type":"agent/inbox/spliced","data":{"target":"next-step","start":0,"inserted":[{"id":"{{messageId}}","role":"user","content":[{"type":"text","text":"Serial agent creation completed. Ordinary and nested forks are independent; historical fork metadata remains readable."}],"source":{"kind":"plugin:serial-created-fixture"}}]}}
 {"type":"agent/inbox/spliced","data":{"target":"next-turn","start":0,"inserted":[{"content":[{"type":"text","text":"Run the advanced packaged-runtime snapshot scenario."}],"source":{"kind":"user"},"role":"user","id":"{{messageId}}"}]}}
 {"type":"turn/start","data":{"turn":1}}
 {"type":"agent/inbox/spliced","data":{"target":"next-step","start":0,"removedCount":1,"inserted":[]}}
 {"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":"{{messageId}}"}},"surfaceOp":"append"}
-{"type":"user/message","data":{"id":"{{messageId}}","role":"user","content":[{"type":"text","text":"Serial agent creation completed."}],"source":{"kind":"plugin:serial-created-fixture"}},"surfaceOp":"append"}
+{"type":"user/message","data":{"id":"{{messageId}}","role":"user","content":[{"type":"text","text":"Serial agent creation completed. Ordinary and nested forks are independent; historical fork metadata remains readable."}],"source":{"kind":"plugin:serial-created-fixture"}},"surfaceOp":"append"}
 {"type":"user/message","data":{"content":[{"type":"text","text":"Run the advanced packaged-runtime snapshot scenario."}],"source":{"kind":"user"},"role":"user","id":"{{messageId}}"},"surfaceOp":"append"}
 {"type":"user/message","data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent working directory: \"{{cwd}}\".\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":"working-directory:current","text":"Current working directory: \"{{cwd}}\"."},{"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":"{{messageId}}"},"surfaceOp":"append"}
 {"type":"user/message","data":{"id":"{{messageId}}","role":"user","content":[{"type":"image","attachment":{"attachmentId":"sha256:b1ff9c8ea3a780bad09b346c423d2d0e46815926879b18e841d928376a946640","mediaType":"image/png","width":1,"height":1,"bytes":69}}],"source":{"kind":"python-snapshot-image-offload"}},"surfaceOp":"append"}

scripts/snapshots/python-sdk-single-exe/advanced/result.json

@@ -98,7 +98,7 @@
         "content": [
           {
             "type": "text",
-            "text": "Serial agent creation completed."
+            "text": "Serial agent creation completed. Ordinary and nested forks are independent; historical fork metadata remains readable."
           }
         ],
         "source": {
@@ -1628,7 +1628,7 @@
             "content": [
               {
                 "type": "text",
-                "text": "Serial agent creation completed."
+                "text": "Serial agent creation completed. Ordinary and nested forks are independent; historical fork metadata remains readable."
               }
             ],
             "source": {

scripts/snapshots/python-sdk-single-exe/advanced/session.v4.jsonl

@@ -2,14 +2,14 @@
 {"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-step","start":0,"inserted":[{"id":"{{messageId}}","role":"user","content":[{"type":"text","text":"Serial agent creation completed."}],"source":{"kind":"plugin:serial-created-fixture"}}]}}
+{"type":"agent/inbox/spliced","data":{"target":"next-step","start":0,"inserted":[{"id":"{{messageId}}","role":"user","content":[{"type":"text","text":"Serial agent creation completed. Ordinary and nested forks are independent; historical fork metadata remains readable."}],"source":{"kind":"plugin:serial-created-fixture"}}]}}
 {"type":"agent/inbox/spliced","data":{"target":"next-turn","start":0,"inserted":[{"content":[{"type":"text","text":"Run the advanced packaged-runtime snapshot scenario."}],"source":{"kind":"user"},"role":"user","id":"{{messageId}}"}]}}
 {"type":"turn/start","data":{"turn":1}}
 {"type":"agent/inbox/spliced","data":{"target":"next-step","start":0,"removedCount":1,"inserted":[]}}
 {"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":"{{messageId}}"}},"surfaceOp":"append"}
-{"type":"user/message","data":{"id":"{{messageId}}","role":"user","content":[{"type":"text","text":"Serial agent creation completed."}],"source":{"kind":"plugin:serial-created-fixture"}},"surfaceOp":"append"}
+{"type":"user/message","data":{"id":"{{messageId}}","role":"user","content":[{"type":"text","text":"Serial agent creation completed. Ordinary and nested forks are independent; historical fork metadata remains readable."}],"source":{"kind":"plugin:serial-created-fixture"}},"surfaceOp":"append"}
 {"type":"user/message","data":{"content":[{"type":"text","text":"Run the advanced packaged-runtime snapshot scenario."}],"source":{"kind":"user"},"role":"user","id":"{{messageId}}"},"surfaceOp":"append"}
 {"type":"user/message","data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent working directory: \"{{cwd}}\".\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":"working-directory:current","text":"Current working directory: \"{{cwd}}\"."},{"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":"{{messageId}}"},"surfaceOp":"append"}
 {"type":"user/message","data":{"id":"{{messageId}}","role":"user","content":[{"type":"image","attachment":{"attachmentId":"sha256:b1ff9c8ea3a780bad09b346c423d2d0e46815926879b18e841d928376a946640","mediaType":"image/png","width":1,"height":1,"bytes":69}}],"source":{"kind":"python-snapshot-image-offload"}},"surfaceOp":"append"}