fix(fable): accept effort markers on a merged user boundary

packages/opencode/src/effort-history.ts

@@ -609,16 +609,16 @@ export function applyOpenCodeEffortMarkers(
   }
 
   for (const message of consumed.messages) {
-    if (message.transitions.length > 1) {
-      throw new EffortMarkerCorrelationError(
-        'Multiple internal Fable 5.1 effort markers on one user boundary',
-      )
-    }
-    const transition = message.transitions[0]
-    if (transition && transition.scope !== requestPlan.scope) {
-      throw new EffortMarkerCorrelationError(
-        'Fable 5.1 effort marker scope mismatch',
-      )
+    // Consecutive host user records collapse into one wire message, so a
+    // boundary may legitimately carry several transitions. The flat checks
+    // below pin their order and identity; every one still needs its scope
+    // verified, not just the first.
+    for (const transition of message.transitions) {
+      if (transition.scope !== requestPlan.scope) {
+        throw new EffortMarkerCorrelationError(
+          'Fable 5.1 effort marker scope mismatch',
+        )
+      }
     }
     if (message.anchors.length > 1) {
       throw new EffortMarkerCorrelationError(
@@ -719,7 +719,7 @@ export function applyOpenCodeEffortMarkers(
   let inserted = 0
   const rewritten: unknown[] = []
   for (const message of consumed.messages) {
-    const transition = message.transitions[0]
+    const transition = message.transitions.at(-1)
     if (transition && applyConfig) {
       rewritten.push({
         role: 'system',

packages/opencode/src/tests/effort-history.test.ts

@@ -579,4 +579,188 @@ describe('OpenCode Fable 5.1 effort markers', () => {
     expect(markOpenCodeEffortTransitions(otherModel)).toBeNull()
     expect(markerTexts(otherModel)).toEqual([])
   })
+
+  test('accepts a merged boundary whose transitions are a correctly-ordered run and emits the last effort', () => {
+    const messages = [
+      user('msg_low', 'ses_merged', 'claude-fable-5-1', 'low'),
+      user('msg_high', 'ses_merged', 'claude-fable-5-1', 'high'),
+      user('msg_max', 'ses_merged', 'claude-fable-5-1', 'max'),
+    ]
+    const plan = markOpenCodeEffortTransitions(messages)
+    expect(plan).not.toBeNull()
+    expect(plan?.markerCount).toBe(2)
+
+    const highMarker = markerTexts([messages[1]!])[0]
+    const maxMarker = markerTexts([messages[2]!])[0]
+    const anchor = messages[2]!.parts
+      .map((part) => part.text)
+      .find((text) => text.startsWith(EFFORT_ANCHOR_PREFIX))
+    expect(highMarker).toBeDefined()
+    expect(maxMarker).toBeDefined()
+    expect(anchor).toBeDefined()
+
+    const body: {
+      model: string
+      output_config: { effort: string }
+      messages: unknown[]
+    } = {
+      model: 'claude-fable-5-1',
+      output_config: { effort: 'low' },
+      messages: [
+        { role: 'user', content: [{ type: 'text', text: 'msg_low' }] },
+        {
+          role: 'user',
+          content: [
+            { type: 'text', text: highMarker },
+            { type: 'text', text: maxMarker },
+            { type: 'text', text: anchor },
+          ],
+        },
+      ],
+    }
+
+    expect(
+      applyOpenCodeEffortMarkers(
+        body,
+        true,
+        encodeOpenCodeEffortPlan(plan as NonNullable<typeof plan>),
+        plan as NonNullable<typeof plan>,
+      ),
+    ).toEqual({ found: 2, inserted: 1 })
+    expect(body.messages).toContainEqual({
+      role: 'system',
+      content: [],
+      output_config: { effort: 'max' },
+    })
+    expect(body.messages).not.toContainEqual({
+      role: 'system',
+      content: [],
+      output_config: { effort: 'high' },
+    })
+    expect(JSON.stringify(body)).not.toContain('cortexkit-internal-effort')
+  })
+
+  test('rejects a merged boundary whose transitions are out of order', () => {
+    const messages = [
+      user('msg_low', 'ses_merged_order', 'claude-fable-5-1', 'low'),
+      user('msg_high', 'ses_merged_order', 'claude-fable-5-1', 'high'),
+      user('msg_max', 'ses_merged_order', 'claude-fable-5-1', 'max'),
+    ]
+    const plan = markOpenCodeEffortTransitions(messages)
+    const highMarker = markerTexts([messages[1]!])[0]
+    const maxMarker = markerTexts([messages[2]!])[0]
+    const anchor = messages[2]!.parts
+      .map((part) => part.text)
+      .find((text) => text.startsWith(EFFORT_ANCHOR_PREFIX))
+    const body = {
+      model: 'claude-fable-5-1',
+      output_config: { effort: 'low' },
+      messages: [
+        { role: 'user', content: [{ type: 'text', text: 'msg_low' }] },
+        {
+          role: 'user',
+          content: [
+            { type: 'text', text: maxMarker },
+            { type: 'text', text: highMarker },
+            { type: 'text', text: anchor },
+          ],
+        },
+      ],
+    }
+
+    expect(() =>
+      applyOpenCodeEffortMarkers(
+        body,
+        true,
+        encodeOpenCodeEffortPlan(plan as NonNullable<typeof plan>),
+        plan as NonNullable<typeof plan>,
+      ),
+    ).toThrow('Fable 5.1 effort marker non-prefix loss')
+  })
+
+  test('rejects a merged boundary whose transitions are duplicated', () => {
+    const messages = [
+      user('msg_low', 'ses_merged_dup', 'claude-fable-5-1', 'low'),
+      user('msg_high', 'ses_merged_dup', 'claude-fable-5-1', 'high'),
+      user('msg_max', 'ses_merged_dup', 'claude-fable-5-1', 'max'),
+    ]
+    const plan = markOpenCodeEffortTransitions(messages)
+    const highMarker = markerTexts([messages[1]!])[0]
+    const maxMarker = markerTexts([messages[2]!])[0]
+    const anchor = messages[2]!.parts
+      .map((part) => part.text)
+      .find((text) => text.startsWith(EFFORT_ANCHOR_PREFIX))
+    const body = {
+      model: 'claude-fable-5-1',
+      output_config: { effort: 'low' },
+      messages: [
+        { role: 'user', content: [{ type: 'text', text: 'msg_low' }] },
+        {
+          role: 'user',
+          content: [
+            { type: 'text', text: highMarker },
+            { type: 'text', text: highMarker },
+            { type: 'text', text: maxMarker },
+            { type: 'text', text: anchor },
+          ],
+        },
+      ],
+    }
+
+    expect(() =>
+      applyOpenCodeEffortMarkers(
+        body,
+        true,
+        encodeOpenCodeEffortPlan(plan as NonNullable<typeof plan>),
+        plan as NonNullable<typeof plan>,
+      ),
+    ).toThrow('Fable 5.1 effort marker correlation failed: expected 2, found 3')
+  })
+
+  test('rejects a foreign-scope marker at index 1 of a merged boundary', () => {
+    const messages = [
+      user('msg_low', 'ses_merged_scope', 'claude-fable-5-1', 'low'),
+      user('msg_high', 'ses_merged_scope', 'claude-fable-5-1', 'high'),
+      user('msg_max', 'ses_merged_scope', 'claude-fable-5-1', 'max'),
+    ]
+    const plan = markOpenCodeEffortTransitions(messages)
+    const highMarker = markerTexts([messages[1]!])[0]
+    const anchor = messages[2]!.parts
+      .map((part) => part.text)
+      .find((text) => text.startsWith(EFFORT_ANCHOR_PREFIX))
+
+    // A valid marker minted for a different session carries a foreign scope.
+    const foreignMessages = [
+      user('msg_foreign_low', 'ses_foreign_scope', 'claude-fable-5-1', 'low'),
+      user('msg_foreign_high', 'ses_foreign_scope', 'claude-fable-5-1', 'high'),
+    ]
+    markOpenCodeEffortTransitions(foreignMessages)
+    const foreignMarker = markerTexts([foreignMessages[1]!])[0]
+    expect(foreignMarker).toBeDefined()
+
+    const body = {
+      model: 'claude-fable-5-1',
+      output_config: { effort: 'low' },
+      messages: [
+        { role: 'user', content: [{ type: 'text', text: 'msg_low' }] },
+        {
+          role: 'user',
+          content: [
+            { type: 'text', text: highMarker },
+            { type: 'text', text: foreignMarker },
+            { type: 'text', text: anchor },
+          ],
+        },
+      ],
+    }
+
+    expect(() =>
+      applyOpenCodeEffortMarkers(
+        body,
+        true,
+        encodeOpenCodeEffortPlan(plan as NonNullable<typeof plan>),
+        plan as NonNullable<typeof plan>,
+      ),
+    ).toThrow('Fable 5.1 effort marker scope mismatch')
+  })
 })

packages/opencode/src/tests/index.test.ts

@@ -65,7 +65,7 @@ import {
 } from '@cortexkit/anthropic-auth-core'
 import { SubcCallError } from '@cortexkit/subc-client'
 import { getOpenCodeClaustrumEnrollmentPaths } from '../claustrum-enrollment-registry'
-import { EFFORT_MARKER_PREFIX } from '../effort-history'
+import { EFFORT_ANCHOR_PREFIX, EFFORT_MARKER_PREFIX } from '../effort-history'
 import { AnthropicAuthPlugin } from '../index'
 import { LANE_START_REQUEST_HEADER, LANE_START_TEXT } from '../lane-start'
 import {
@@ -10542,6 +10542,9 @@ describe('Fable 5.1 request-scoped effort history', () => {
     const transitionMarker = internalTexts?.find((text) =>
       text.startsWith(EFFORT_MARKER_PREFIX),
     )
+    const anchorMarker = internalTexts?.find((text) =>
+      text.startsWith(EFFORT_ANCHOR_PREFIX),
+    )
     expect(transitionMarker).toBeString()
     const correlatedHeaders = { headers: {} as Record<string, string> }
     await plugin['chat.headers'](
@@ -10612,10 +10615,11 @@ describe('Fable 5.1 request-scoped effort history', () => {
     const duplicateTransition = await send('ses_effort_duplicate_transition', [
       transitionMarker,
       transitionMarker,
+      anchorMarker,
     ])
     expect(duplicateTransition.status).toBe(400)
     expect((await duplicateTransition.json()).error.message).toBe(
-      'Multiple internal Fable 5.1 effort markers on one user boundary',
+      'Fable 5.1 effort marker correlation failed: expected 1, found 2',
     )
     expect(messagesCalled).toBe(false)
   })