feat(session): refuse session logs a build cannot faithfully read

Old runtimes meeting a newer session format now fail loud instead of
misreading: version refusal names the direction (newer: upgrade the
harness; older: no upgrade path) and points at the raw JSONL log, and an
event type outside the generated known vocabulary refuses resume unless
its envelope carries the new ignorable: true marker (default: required,
so a forgotten marker over-refuses instead of silently resuming a gutted
session). gen-persistence-catalog now also emits
KNOWN_SESSION_EVENT_TYPES; SQLite stores the marker in a dedicated
column (SCHEMA_VERSION 15). The versioning design (monotonic integer,
n->n+1 upgrader chain, migrate-on-continue) is recorded in the
session-log-version-mechanism Agent Note.

packages/core/session/src/index.ts

@@ -32,6 +32,7 @@ export type { ChunkRow, StorageRecord } from './chunk-rows.ts'
 export type { SessionSurface, SurfaceFoldReplacement, SurfaceFoldResult } from './surface.ts'
 export { deriveEventMessage, foldSurface, isAppendSurfaceEvent, isReplacementSurfaceEvent, isSurfaceEvent, isSurfaceEligibleType } from './surface.ts'
 export { canonicalHeader, foldRequestHeader, headerEquals } from './request-header.ts'
+export { KNOWN_SESSION_EVENT_TYPES } from './known-event-types.ts'
 
 /**
  * Find the latest closed turn that entered at least one model step, ignoring
@@ -243,6 +244,7 @@ function assertSessionEventEnvelope(value: Record<string, unknown>, index: numbe
       case 'data':
       case 'surfaceOp':
       case 'sourceEventSeqs':
+      case 'ignorable':
         break
       default:
         throw new Error(`seed event at index ${index} has an invalid event envelope`)
@@ -254,7 +256,8 @@ function assertSessionEventEnvelope(value: Record<string, unknown>, index: numbe
   if (typeof type !== 'string'
     || typeof seq !== 'number' || !Number.isSafeInteger(seq) || seq < 0
     || typeof time !== 'number' || !Number.isSafeInteger(time)
-    || event['data'] === undefined) {
+    || event['data'] === undefined
+    || (event['ignorable'] !== undefined && event['ignorable'] !== true)) {
     throw new Error(`seed event at index ${index} has an invalid event envelope`)
   }
   switch (type) {