Merge remote-tracking branch 'origin/master' into xtr/agent-loop-message-machine

# Conflicts:
#	docs/cordis-catalog/services.md
#	docs/core-data-structures/session.i18n.yaml
#	docs/event-producer-consumer.md
#	examples/acp-agent/tests/snapshots/cordis-inspect-jsdoc/session.jsonl

packages/core/session/src/index.ts

@@ -296,6 +296,19 @@ export class Session {
     return this.header.id
   }
 
+  /**
+   * The first seq appended IN THIS PROCESS: the length of the constructor
+   * seed (0 without one). Events below it entered through construction —
+   * replay, fork, or resume — and were never published on the `session/event`
+   * firehose (constructor seeds do not emit), so consumers that replay the
+   * log as a publication substitute (telemetry adoption) start here. Distinct
+   * from `header.seedLength`, the DURABLE fork-lineage boundary: a resumed
+   * session's constructor seed is its full stored log, while its header keeps
+   * the original fork value — this field is the in-process construction fact
+   * and is deliberately not persisted.
+   */
+  readonly firstLiveSeq: number
+
   constructor(id: SessionId, seed?: readonly SessionEvent[], header?: SessionHeader) {
     if (seed) {
       // Validate the seed to the SAME invariants `append` enforces, so a
@@ -328,6 +341,7 @@ export class Session {
         this.log.push(deepFreeze(snapshot))
       }
     }
+    this.firstLiveSeq = this.log.length
     this.header = snapshotSessionHeader(id, header)
   }