Merge branch 'master' of https://github.com/deepseek-harness/deepseek-harness into xtr/react-loop-simplification

# Conflicts:
#	.agents/notes/implemented/feature/2026-07-17-dedicated-full-screen-tui-front-door.i18n.yaml
#	docs/architecture.i18n.yaml
#	docs/cookbook/extension-cookbook.i18n.yaml
#	docs/cordis-catalog/events.md
#	docs/cordis-catalog/services.md
#	docs/core-data-structures/core.i18n.yaml
#	docs/core-data-structures/core.md
#	docs/core-data-structures/core.zh.md
#	docs/core-data-structures/llm-streaming.i18n.yaml
#	docs/core-data-structures/llm-streaming.md
#	docs/core-data-structures/llm-streaming.zh.md
#	docs/core-data-structures/session.i18n.yaml
#	docs/event-producer-consumer.md
#	docs/persistence-catalog.md
#	packages/cordis/tool-cordis/src/api-catalog.ts
#	packages/core/agent-loop/README.i18n.yaml
#	packages/core/agent-loop/src/agent.ts
#	packages/core/agent/README.i18n.yaml
#	packages/core/session/README.i18n.yaml
#	packages/core/session/src/types.ts
#	packages/llm/llm/README.i18n.yaml
#	packages/llm/llm/README.md
#	packages/llm/llm/README.zh.md
#	packages/llm/llm/src/index.ts
#	packages/llm/llm/tests/service.spec.ts
#	packages/sdk/sdk-client/README.i18n.yaml
#	packages/sdk/sdk-protocol/README.i18n.yaml
#	packages/sdk/sdk-protocol/README.md
#	packages/sdk/sdk-protocol/README.zh.md
#	packages/subagent/subagent-dsh-sdk/README.i18n.yaml
#	packages/ui/jsonrpc/README.i18n.yaml
#	packages/ui/jsonrpc/README.md
#	packages/ui/jsonrpc/README.zh.md
#	packages/ui/tui/src/index.ts
#	python/sdk/README.i18n.yaml
#	scripts/gen-cordis-catalog.ts

packages/core/session/tests/surface.spec.ts

@@ -4,6 +4,8 @@ import {
   Session,
   SessionId,
   foldSurface,
+  isAppendSurfaceEvent,
+  isReplacementSurfaceEvent,
   isSurfaceEligibleType,
   isSurfaceEvent,
 } from '@deepseek-ai/dsh-session'
@@ -861,6 +863,40 @@ describe('surface type guards', () => {
     expect(isSurfaceEligibleType(markerless.type)).toBe(true)
     expect(isSurfaceEvent(markerless)).toBe(false)
   })
+
+  it('splits surface events into append-origin and replacement by their marker', () => {
+    const s = surfaceSession()
+    s.append('user/message', createUserMessage({
+      content: [{ type: 'text', text: 'checkpoint' }], source: { kind: 'plugin', plugin: 'compact' },
+    }), { surfaceOp: { op: 'replace', start: 1, end: 2 }, sourceEventSeqs: [1, 2] })
+    const appended = s.events.find(e => e.type === 'user/message')!
+    const replacement = s.events.at(-1)!
+
+    expect(isAppendSurfaceEvent(appended)).toBe(true)
+    expect(isReplacementSurfaceEvent(appended)).toBe(false)
+    expect(isAppendSurfaceEvent(replacement)).toBe(false)
+    expect(isReplacementSurfaceEvent(replacement)).toBe(true)
+  })
+
+  it('rejects log-only and markerless events from both marker guards', () => {
+    const s = surfaceSession()
+    const turnStart = s.events.find(e => e.type === 'turn/start')!
+    // A surface-eligible type whose mandatory marker is absent has no origin at
+    // all: it never entered the surface.
+    const markerless: SessionEvent = {
+      type: 'user/message',
+      seq: 0,
+      time: 0,
+      data: createUserMessage({
+        content: [{ type: 'text', text: 'hi' }], source: { kind: 'user' },
+      }),
+    }
+
+    expect(isAppendSurfaceEvent(turnStart)).toBe(false)
+    expect(isReplacementSurfaceEvent(turnStart)).toBe(false)
+    expect(isAppendSurfaceEvent(markerless)).toBe(false)
+    expect(isReplacementSurfaceEvent(markerless)).toBe(false)
+  })
 })
 
 describe('SurfaceManager.replaceGeneration', () => {