Merge origin/master into worktree/deepseek-max-tokens-defaults

# Conflicts:
#	docs/cordis-catalog/services.md
#	docs/core-data-structures/core.i18n.yaml
#	docs/core-data-structures/session.i18n.yaml
#	packages/core/session/README.i18n.yaml

packages/core/session/src/index.ts

@@ -27,7 +27,7 @@ export { interruptedTurnClosers, lastActivityTime, TOOL_NOT_STARTED, TOOL_OUTCOM
 export { decodeStorageRecord, packChunkRuns } from './chunk-rows.ts'
 export type { ChunkRow, StorageRecord } from './chunk-rows.ts'
 export type { SessionSurface, SurfaceFoldReplacement, SurfaceFoldResult } from './surface.ts'
-export { foldSurface, isSurfaceEvent, isSurfaceEligibleType } from './surface.ts'
+export { foldSurface, isAppendSurfaceEvent, isReplacementSurfaceEvent, isSurfaceEvent, isSurfaceEligibleType } from './surface.ts'
 export { canonicalHeader, foldRequestHeader, headerEquals } from './request-header.ts'
 
 /**
@@ -505,7 +505,8 @@ export class Session {
    *   the ordered surface; `sourceEventSeqs` records provenance (the seq
    *   numbers of events this one derives from). REQUIRED for
    *   {@link SurfaceEventType} events (every message-producing event must
-   *   declare how it joins the surface, the sole source of derived history) and
+   *   declare how it joins the surface, the sole source of derived model
+   *   history) and
    *   rejected by the compiler for non-surface types like `turn/start` or
    *   `assistant/chunk`.
    * @returns the logged event — its assigned `seq`/`time` plus the SNAPSHOT of

packages/core/session/src/surface.ts

@@ -37,6 +37,36 @@ export function isSurfaceEvent(event: SessionEvent): event is SurfaceEvent {
   return (event as SessionEvent<SurfaceEventType>).surfaceOp !== undefined
 }
 
+/**
+ * Narrow an event to an append-origin surface event: one that entered the
+ * surface at its own log position and was never itself a replacement copy.
+ *
+ * The model-visible surface deliberately shadows replaced ranges, so it is the
+ * wrong source for a human transcript — a landed replacement would erase
+ * conversation the user already saw. Append-origin events are that transcript's
+ * durable source material; replacement copies stay model-only.
+ * @param event - event to test.
+ * @returns true when the event appended to the surface tail.
+ */
+export function isAppendSurfaceEvent(
+  event: SessionEvent,
+): event is SurfaceEvent & { surfaceOp: 'append' } {
+  return isSurfaceEvent(event) && event.surfaceOp === 'append'
+}
+
+/**
+ * Narrow an event to a surface replacement: a node that shadowed an existing
+ * surface range instead of appending to the tail. The counterpart of
+ * {@link isAppendSurfaceEvent} over the two {@link SurfaceOp} variants.
+ * @param event - event to test.
+ * @returns true when the event replaced a surface range.
+ */
+export function isReplacementSurfaceEvent(
+  event: SessionEvent,
+): event is SurfaceEvent & { surfaceOp: Extract<SurfaceOp, { op: 'replace' }> } {
+  return isSurfaceEvent(event) && event.surfaceOp !== 'append'
+}
+
 /** One replacement operation observed while folding a session surface. */
 export interface SurfaceFoldReplacement {
   /** Seq of the event that replaced the prior surface range. */