fix(sdk): persist injected context alongside a compaction

saveTranscript made compaction and injections mutually exclusive in the
persisted runtime state, but restoreModelLane treats them independently:
injections anchored past a valid compaction apply on top, and if the
compaction fingerprint fails to match at boot the whole compacted lane is
discarded. In that case a same-turn injection that only lived in the
dropped `injections` field was lost. Emit both fields; restore already
filters injections that a valid compaction covers, so there is no
double-apply.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VG39FXXkFFU24U5EtJMwPi

Author: ericallam

packages/trigger-sdk/src/v3/ai.ts

@@ -7171,9 +7171,8 @@ function chatAgent<
                         fingerprint: prefixFingerprint(shadow, throughId),
                       },
                     }
-                  : laneInjections.length > 0
-                    ? { injections: laneInjections }
-                    : {}),
+                  : {}),
+                ...(laneInjections.length > 0 ? { injections: laneInjections } : {}),
                 ...(queued.length > 0 ? { queued: [...queued] } : {}),
               }
             : null;

packages/trigger-sdk/test/transcript-changesets.test.ts

@@ -547,4 +547,53 @@ describe("restoreModelLane", () => {
     expect(restored.compacted).toBe(false);
     expect(restored.messages.map((m) => m.content)).toEqual(["u-1", "a-1", "u-2"]);
   });
+
+  it("applies persisted injections when the compacted lane is invalidated", async () => {
+    const state = {
+      v: 1 as const,
+      compaction: {
+        modelMessages: [{ role: "assistant" as const, content: "STALE SUMMARY" }],
+        throughId: "gone",
+        fingerprint: "does-not-match",
+      },
+      injections: [
+        {
+          afterId: "",
+          messages: [{ role: "user" as const, content: "[note] survives compaction loss" }],
+        },
+      ],
+    };
+    const restored = await restoreModelLane([userMessage("kept", "k-1")], state, async (messages) =>
+      messages.map((m) => ({ role: m.role, content: m.id }) as never)
+    );
+    expect(restored.compacted).toBe(false);
+    const dump = JSON.stringify(restored.messages);
+    expect(dump).toContain("[note] survives compaction loss");
+    expect(dump).not.toContain("STALE SUMMARY");
+  });
+
+  it("does not re-apply an injection a valid compaction already covers", async () => {
+    const shadow = createTranscriptShadow([userMessage("one", "u-1")]);
+    const state = {
+      v: 1 as const,
+      compaction: {
+        modelMessages: [{ role: "assistant" as const, content: "SUMMARY WITH THE NOTE BAKED IN" }],
+        throughId: "u-1",
+        fingerprint: prefixFingerprint(shadow, "u-1"),
+      },
+      injections: [
+        {
+          afterId: "u-1",
+          messages: [{ role: "user" as const, content: "[note] already in the summary" }],
+        },
+      ],
+    };
+    const restored = await restoreModelLane([userMessage("one", "u-1")], state, async (messages) =>
+      messages.map((m) => ({ role: m.role, content: m.id }) as never)
+    );
+    expect(restored.compacted).toBe(true);
+    const dump = JSON.stringify(restored.messages);
+    expect(dump).toContain("SUMMARY WITH THE NOTE BAKED IN");
+    expect(dump).not.toContain("[note] already in the summary");
+  });
 });