diff --git a/packages/context/session-reference/src/index.ts b/packages/context/session-reference/src/index.ts
index 8110f4ead6..433ee1d0b1 100644
--- a/packages/context/session-reference/src/index.ts
+++ b/packages/context/session-reference/src/index.ts
@@ -138,9 +138,11 @@ export class SessionReferenceResolver extends TypertRemoteService {
       if (references.length === 0) return [message]
       const resolved = await this.prepare(agent, content, references, signal)
       const direct = freezeMessage({ ...message, content: resolved.content })
-      return resolved.additionalContext === undefined
-        ? [direct]
-        : [resolved.additionalContext, direct]
+      /* v8 ignore if -- a parsed canonical mention always leaves one normalized reference */
+      if (resolved.additionalContext === undefined) {
+        throw new Error('session-reference preparation omitted context for a canonical mention')
+      }
+      return [resolved.additionalContext, direct]
     }))
     return prepared.flat()
   }
diff --git a/packages/context/session-reference/tests/session-reference.spec.ts b/packages/context/session-reference/tests/session-reference.spec.ts
index 357e8bb0a6..e1eac75658 100644
--- a/packages/context/session-reference/tests/session-reference.spec.ts
+++ b/packages/context/session-reference/tests/session-reference.spec.ts
@@ -314,7 +314,7 @@ describe('session reference discovery and preparation', () => {
       content: [{
         type: 'text',
         text: `compare ${formatSessionReferenceMention({ sessionId: source.id, label: 'Research' })} now`,
-      }],
+      }, { type: 'reasoning', text: 'preserve this non-text block' }],
       source: { kind: 'user' },
     })
     const ordinary = createUserMessage({
@@ -342,7 +342,10 @@ describe('session reference discovery and preparation', () => {
     })
     expect(decision.messages[1]).toMatchObject({
       id: direct.id,
-      content: [{ type: 'text', text: 'compare @Research now' }],
+      content: [
+        { type: 'text', text: 'compare @Research now' },
+        { type: 'reasoning', text: 'preserve this non-text block' },
+      ],
     })
     expect(decision.messages[1]).not.toBe(direct)
     expect(decision.messages[2]).toBe(ordinary)