spec: session-2.md — v2 write model, sync semantics and default-store rules

CHANGELOG.md

@@ -266,6 +266,74 @@ version 2: its `{{ … }}` sequences become substitution points, and its
 
 ## OVOS-SESSION-2 — Session Lifecycle and State Ownership
 
+### 2
+
+Version 2 is **not compatible with version 1**. Version 1 left
+the write model under-determined: the two write paths onto the
+default session were not distinguished, no ordering was defined
+across the four in-utterance write paths, and `ovos.session.sync`
+was simultaneously required to reach terminal events (§2.7) and
+forbidden to mutate session mid-utterance (§2.6). An
+implementation built against version 1 can satisfy version 1 and
+violate version 2.
+
+- §2.6 — `ovos.session.sync` carved out of the
+  incidental-bus-event rule that previously contradicted §2.7.
+  The visibility split is now stated: a merged sync reaches
+  terminal-event snapshots and any matcher or hook not yet run,
+  and never revises a snapshot a consumer already holds.
+- §2.6 — the handler-boundary in-place path is bounded to fields
+  the handler owns and cites OVOS-MSG-1 §4.1's owned-field
+  allowance as what makes it conformant. The
+  `Match.updated_session` commit mechanic is now cited to
+  PIPELINE-1 §4.2 rather than restated.
+- §2.7 — field replacement stated as the default merge rule,
+  with claiming specifications permitted to define a finer
+  intra-field merge; `session.intent_context` named as the one
+  such field at this version (OVOS-CONTEXT-1 §5.3).
+- §2.7 — a sync on a named session with no utterance in flight
+  is an orchestrator no-op; the owning client still consumes it.
+  Nested lifecycles bind the innermost lifecycle in flight
+  (PIPELINE-1 §6.5).
+- §2.8 (new) — normative write-ordering timeline across the
+  inbound merge, transformer hooks, match-phase writes,
+  dispatch-time orchestrator writes and handler/sync writes,
+  plus last-writer-wins resolved **per field**, its two
+  exceptions, and the statement that unorderable ties have no
+  defined winner.
+- §3.2 — "latest received" retired as a client policy: the bus
+  guarantees no order. Adoption at `ovos.utterance.handled` is
+  RECOMMENDED; incremental adoption stays a MAY, with an
+  explicit staleness warning and a SHOULD to converge at §3.3.
+- §5.1 — the omitted-field-leaves-stored-value rule is owned as
+  a deliberate deviation from SESSION-1 §2.1, confined to writes
+  into the default-session store; the false attribution of the
+  rule to SESSION-1 §2.1 is dropped.
+- §5.1 — default-store write acceptance: the orchestrator merges
+  a session-less inbound Message into the store only from a
+  local source, with OVOS-BRIDGE-1 §3.4 named as the enforcement
+  point for relayed traffic. SESSION-1 §2.4 field tolerance
+  stated as applying at store-write.
+- §5.1 — the match-pathway wholesale replacement now says a
+  field absent from `Match.updated_session` **reverts to the
+  deployment default at consumption**, not that it is deleted,
+  and carves out the PIPELINE-1 §7.1 `active_handlers` push and
+  the OVOS-CONTEXT-1 §5.3 entry-level `intent_context` merge.
+- §5.4 folded into §7 as a non-normative deployment note; the
+  end-marker citation is pinned to PIPELINE-1 §9.5 throughout.
+- RFC 2119 usage — "MUST NOT be expected to" reworded as
+  behaviour required of a named actor (§2.2, §2.4, §2.6, §6.4).
+- Descriptive passages in §2.3, §2.4, §2.5, §4.3 and §5.2 marked
+  informative.
+- §2.4 / §6.3 — clarified that only a specification claims a
+  field (SESSION-1 §2.2); a component projecting into an
+  unclaimed field rides SESSION-1 §2.4 tolerance and gets no
+  normative reading from anyone else.
+- Citations — SESSION-1 registry claims corrected to §2.2 (§2.4,
+  §7); restart-loss citation corrected to §5.2; companion-spec
+  count corrected to six; CONTEXT-1/CONVERSE-1 field attribution
+  in the intro untangled.
+
 ### 1
 
 - The state-ownership model (stateless bus, stateless orchestrator for