test(snapshot): share identical header sidecars

packages/support/acp-snapshot/tests/fixtures/suite/shared-pin/behavior.json

@@ -0,0 +1,12 @@
+{
+  "prompt": "respond",
+  "logs": [{
+    "file": "b/main/session.jsonl",
+    "lines": [
+      { "type": "session", "id": "{{SID}}", "createdAt": 100, "cwd": "{{CWD}}", "delegationDepth": 0 },
+      { "type": "request/header", "seq": 0, "time": 100, "data": { "header": { "config": { "model": "fake" }, "system": "SYS PROMPT", "tools": [{ "name": "t1", "description": "D1", "parameters": { "type": "object" } }] }, "reason": "initial" } },
+      { "type": "request/header", "seq": 1, "time": 100, "data": { "header": { "config": { "model": "fake" }, "system": "SYS PROMPT\n\nNEW PROMPT LINE", "tools": [{ "name": "t1", "description": "D1", "parameters": { "type": "object" } }] }, "reason": "change" } },
+      { "type": "turn/start", "seq": 2, "time": 100, "data": { "turn": 1 } }
+    ]
+  }]
+}

packages/support/acp-snapshot/tests/fixtures/suite/shared-pin/input.json

@@ -0,0 +1 @@
+{ "steps": [{ "op": "initialize" }, { "op": "newSession" }, { "op": "prompt", "text": "pin" }] }

packages/support/acp-snapshot/tests/fixtures/suite/shared-pin/session.jsonl

@@ -0,0 +1,4 @@
+{"type":"session","id":"13131313-3434-4545-8686-787878787878","createdAt":7,"cwd":"/rec/shared-pin-cwd","delegationDepth":0}
+{"type":"request/header","seq":0,"time":7,"data":{"header":{"config":{"model":"fake"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
+{"type":"request/header","seq":1,"time":7,"data":{"header":{"config":{"model":"fake"},"system":"{{system}}","tools":"{{tools}}"},"reason":"change"}}
+{"type":"turn/start","seq":2,"time":7,"data":{"turn":1}}

packages/support/acp-snapshot/tests/fixtures/suite/shared-pin/stdout.expected.jsonl

@@ -0,0 +1,4 @@
+{"jsonrpc":"2.0","id":1,"result":{"protocolVersion":1,"agentCapabilities":{"loadSession":false}}}
+{"jsonrpc":"2.0","id":2,"result":{"sessionId":"{{sessionId}}"}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"thinking about it"}}}}
+{"jsonrpc":"2.0","id":3,"result":{"stopReason":"end_turn"}}