fix: reject legacy session events on every path

packages/session-persistence/session-persistence/src/coordinator.ts

@@ -251,11 +251,15 @@ export class PersistenceCoordinator<TornMarker = unknown> {
     if (batch === undefined) {
       throw new TypeError('session event batch is not losslessly JSON-serializable because it contains non-JSON-serializable data')
     }
-    assertSupportedEvents(batch, id)
     return this.serialize(id, () => this.appendCore(id, batch))
   }
 
   private async appendCore(id: SessionId, events: readonly SessionEvent[]): Promise<void> {
+    // Every append route converges here: the public service, live write-behind
+    // drains, and HMR seed/suffix adoption. Keep vocabulary rejection at that
+    // shared boundary so a stale JavaScript plugin cannot persist an event that
+    // this same backend will refuse to load.
+    assertSupportedEvents(events, id)
     if (events.length === 0) return
     let state = this.states.get(id)
     if (state === undefined) state = await this.adopt(id) // calls loadCore, not load
@@ -528,6 +532,7 @@ export class PersistenceCoordinator<TornMarker = unknown> {
   private async adoptLivePrefix(session: Session, seed: readonly SessionEvent[], stored: StoredPrefix<TornMarker>): Promise<void> {
     const { meta, events, tornMarker } = stored
     this.assertVersion(meta)
+    assertSupportedEvents(events, session.header.id)
     if (!seedCoversPrefix(seed, events)) {
       throw new Error(`session "${session.header.id}" already has a persisted log on disk that does not match this live session (id collision)`)
     }

packages/session-persistence/session-persistence/tests/persistence.spec.ts

@@ -12,6 +12,16 @@ import { runCoordinatorContract, type CoordinatorFixture } from './coordinator-c
 /** The durable store shape: materialized sessions only (no lazy entries). */
 type MemoryStore = Map<string, { meta: SessionHeader; events: SessionEvent[] }>
 
+/** An obsolete event fixture that emulates an untyped pre-change producer. */
+function legacyHeaderDelta(seq = 0): SessionEvent {
+  return {
+    type: 'request/header-delta',
+    seq,
+    time: 1,
+    data: { config: { model: 'legacy' } },
+  } as unknown as SessionEvent
+}
+
 /** Optional plugin config: an EXTERNAL store shared across backend instances. */
 interface MemoryConfig { store?: MemoryStore }
 
@@ -164,4 +174,37 @@ describe('SessionPersistence service registration', () => {
       .rejects.toThrow('session metadata must be losslessly JSON-serializable')
     await fiber.dispose()
   })
+
+  it('rejects a legacy header delta buffered by a pre-change live producer', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const fiber = await ctx.plugin(MemoryPersistence)
+    const session = ctx.sessions.create(SessionId('legacy-live'), { meta: { cwd: '/legacy' } })
+    // Model the runtime shape available to JavaScript or a hot-loaded plugin
+    // compiled against the obsolete event vocabulary.
+    const appendLegacy = session.append.bind(session) as (type: string, data: unknown) => SessionEvent
+    appendLegacy('request/header-delta', { config: { model: 'legacy' } })
+
+    await expect(ctx.sessions.flush(session))
+      .rejects.toThrow(/unsupported legacy request\/header-delta event at seq 0/)
+    await fiber.dispose()
+  })
+
+  it('rejects a legacy stored prefix during live HMR adoption', async () => {
+    const id = SessionId('legacy-hmr')
+    const m = meta(id, '/legacy')
+    const legacy = legacyHeaderDelta()
+    const store: MemoryStore = new Map([[id, { meta: m, events: [legacy] }]])
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    // A current live session cannot carry the obsolete event in its seed, but
+    // HMR still has to identify the persisted prefix as unsupported rather than
+    // treating it as an ordinary live-prefix collision.
+    const session = ctx.sessions.create(id, { meta: { cwd: '/legacy' } })
+    const fiber = await ctx.plugin(MemoryPersistence, { store })
+
+    await expect(ctx.sessions.flush(session))
+      .rejects.toThrow(/unsupported legacy request\/header-delta event at seq 0/)
+    await Promise.allSettled([fiber.dispose()])
+  })
 })

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

@@ -253,7 +253,7 @@
             "workflow"
           ]
         },
-        "reason": "fallback"
+        "reason": "change"
       }
     },
     {
@@ -916,22 +916,29 @@
       }
     },
     {
-      "type": "request/header-delta",
+      "type": "request/header",
       "seq": 56,
       "time": 0,
       "data": {
-        "system": {
-          "keepStart": 62,
-          "keepEnd": 34,
-          "insert": []
+        "header": {
+          "config": {
+            "model": "smoke-model"
+          },
+          "system": "{{system}}",
+          "tools": [
+            "bash",
+            "bash_kill",
+            "bash_output",
+            "cordis_inspect",
+            "cordis_mount",
+            "cordis_unmount",
+            "run_code",
+            "skill",
+            "subagent",
+            "workflow"
+          ]
         },
-        "tools": {
-          "added": [],
-          "removed": [
-            "snapshot_double"
-          ],
-          "changed": []
-        }
+        "reason": "change"
       }
     },
     {
@@ -1397,7 +1404,7 @@
                 "workflow"
               ]
             },
-            "reason": "fallback"
+            "reason": "change"
           }
         }
       }
@@ -2360,22 +2367,29 @@
       "payload": {
         "sessionId": "{{parent}}",
         "event": {
-          "type": "request/header-delta",
+          "type": "request/header",
           "seq": 56,
           "time": 0,
           "data": {
-            "system": {
-              "keepStart": 62,
-              "keepEnd": 34,
-              "insert": []
+            "header": {
+              "config": {
+                "model": "smoke-model"
+              },
+              "system": "{{system}}",
+              "tools": [
+                "bash",
+                "bash_kill",
+                "bash_output",
+                "cordis_inspect",
+                "cordis_mount",
+                "cordis_unmount",
+                "run_code",
+                "skill",
+                "subagent",
+                "workflow"
+              ]
             },
-            "tools": {
-              "added": [],
-              "removed": [
-                "snapshot_double"
-              ],
-              "changed": []
-            }
+            "reason": "change"
           }
         }
       }

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

@@ -13,7 +13,7 @@
 {"type":"tool/result","seq":11,"time":0,"data":{"turn":1,"step":1,"callId":"advanced-mount","content":[{"type":"text","text":"mounted dyn-1 (plugin \"<anonymous>\", state: active)"}],"isError":false},"sourceEventSeqs":[10],"surfaceOp":"append"}
 {"type":"step/end","seq":12,"time":0,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":13,"time":0,"data":{"turn":1,"step":2}}
-{"type":"request/header","seq":14,"time":0,"data":{"header":{"config":{"model":"smoke-model"},"system":"{{system}}","tools":["bash","bash_kill","bash_output","cordis_inspect","cordis_mount","cordis_unmount","run_code","skill","snapshot_double","subagent","workflow"]},"reason":"fallback"}}
+{"type":"request/header","seq":14,"time":0,"data":{"header":{"config":{"model":"smoke-model"},"system":"{{system}}","tools":["bash","bash_kill","bash_output","cordis_inspect","cordis_mount","cordis_unmount","run_code","skill","snapshot_double","subagent","workflow"]},"reason":"change"}}
 {"type":"assistant/chunk","seq":15,"time":0,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
 {"type":"assistant/chunk","seq":16,"time":0,"data":{"turn":1,"step":2,"chunk":{"type":"tool-call-delta","index":0,"id":"advanced-code","name":"run_code","argumentsDelta":"{\"code\": \"return await tools.snapshot_double({ value: 21 })\"}"}}}
 {"type":"assistant/chunk","seq":17,"time":0,"data":{"turn":1,"step":2,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"advanced-code","name":"run_code","arguments":"{\"code\": \"return await tools.snapshot_double({ value: 21 })\"}"}}}}
@@ -55,7 +55,7 @@
 {"type":"tool/result","seq":53,"time":0,"data":{"turn":1,"step":5,"callId":"advanced-unmount","content":[{"type":"text","text":"unmounted dyn-1 (plugin \"<anonymous>\")"}],"isError":false},"sourceEventSeqs":[52],"surfaceOp":"append"}
 {"type":"step/end","seq":54,"time":0,"data":{"turn":1,"step":5}}
 {"type":"step/start","seq":55,"time":0,"data":{"turn":1,"step":6}}
-{"type":"request/header-delta","seq":56,"time":0,"data":{"system":{"keepStart":62,"keepEnd":34,"insert":[]},"tools":{"added":[],"removed":["snapshot_double"],"changed":[]}}}
+{"type":"request/header","seq":56,"time":0,"data":{"header":{"config":{"model":"smoke-model"},"system":"{{system}}","tools":["bash","bash_kill","bash_output","cordis_inspect","cordis_mount","cordis_unmount","run_code","skill","subagent","workflow"]},"reason":"change"}}
 {"type":"assistant/chunk","seq":57,"time":0,"data":{"turn":1,"step":6,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}
 {"type":"assistant/chunk","seq":58,"time":0,"data":{"turn":1,"step":6,"chunk":{"type":"text-delta","index":0,"text":"ADVANCED_EXECUTABLE_OK"}}}
 {"type":"assistant/chunk","seq":59,"time":0,"data":{"turn":1,"step":6,"chunk":{"type":"block-end","index":0,"block":{"type":"text","text":"ADVANCED_EXECUTABLE_OK"}}}}