fix(acp): agents get T3's runtime notes once per session, not on every message

apps/server/scripts/acp-mock-agent.ts

@@ -83,6 +83,10 @@ const failPromptOrdinal = Number(process.env.T3_ACP_FAIL_PROMPT_ORDINAL);
 const compactionPromptOrdinals = new Set(
   (process.env.T3_ACP_COMPACTION_PROMPT_ORDINALS ?? "").split(",").map(Number),
 );
+// These prompts end while their compaction is still in progress.
+const openCompactionPromptOrdinals = new Set(
+  (process.env.T3_ACP_OPEN_COMPACTION_PROMPT_ORDINALS ?? "").split(",").map(Number),
+);
 const failSetModeConfigOption = process.env.T3_ACP_FAIL_SET_MODE_CONFIG_OPTION === "1";
 const emitEmptyDefaultAgentOption = process.env.T3_ACP_EMIT_EMPTY_DEFAULT_AGENT_OPTION === "1";
 const promptResponseText = process.env.T3_ACP_PROMPT_RESPONSE_TEXT;
@@ -1369,6 +1373,16 @@ const program = Effect.gen(function* () {
         yield* Effect.sleep(`${promptDelayMs} millis`);
       }
 
+      if (openCompactionPromptOrdinals.has(promptCount)) {
+        yield* agent.client.sessionUpdate({
+          sessionId: requestedSessionId,
+          update: {
+            sessionUpdate: "compaction_update",
+            compactionId: `compact-${promptCount}`,
+            status: "in_progress",
+          },
+        });
+      }
       if (compactionPromptOrdinals.has(promptCount)) {
         for (const status of ["in_progress", "completed"] as const) {
           yield* agent.client.sessionUpdate({

apps/server/src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts

@@ -1490,7 +1490,7 @@ describe("AcpRegistryAdapterV2", () => {
                   })
                 : "test prompt",
           },
-          runtimeInstructions,
+          ...(ordinal === 1 ? [runtimeInstructions] : []),
         ];
         const echo = (messageId: string, content: ReadonlyArray<unknown>) =>
           claudeFrames.update(CLAUDE_ROOT_SESSION, {
@@ -1511,6 +1511,7 @@ describe("AcpRegistryAdapterV2", () => {
               {
                 type: "text",
                 text: promptText(ordinal),
+                annotations: { audience: ["user"] },
               },
             ]),
             ...(ordering === "before" ? [matching, acknowledgment] : [acknowledgment, matching]),

apps/server/src/orchestration-v2/Adapters/AntigravityAdapterV2.ts

@@ -214,7 +214,7 @@ export function makeAntigravityAcpAdapterFlavor(
     mcpOverHttp: true,
     sessionCarriesPullRequestLinking: antigravityAppendsSystemPrompt,
     makeRuntime,
-    buildPrompt: ({
+    buildAttachmentPrompt: ({
       text,
       attachments,
       resolveAttachmentPath,
@@ -230,6 +230,7 @@ export function makeAntigravityAcpAdapterFlavor(
         agentVersion,
         currentModel,
       }).pipe(
+        Effect.map((blocks) => (text.trim() ? blocks.slice(1) : blocks)),
         Effect.provideService(FileSystem.FileSystem, options.fileSystem),
         Effect.provideService(Path.Path, options.path),
       ),

apps/server/src/orchestration-v2/testkit/ReplayRuntimeInstructions.ts

@@ -20,10 +20,102 @@ export function materializeReplayTranscriptRuntimeInstructions(
               : undefined;
   if (harness === undefined) return transcript;
   const instructions = buildRuntimeInstructions({ harness, model: runtime.model });
+  // The notes name the model, so each prompt expects the ones for its session's current model.
+  const sessionModels = new Map<unknown, string>();
+  const notesFor = (sessionId: unknown) => {
+    const model = sessionModels.get(sessionId) ?? runtime.model;
+    return model === runtime.model ? instructions : buildRuntimeInstructions({ harness, model });
+  };
+  // Grok's flavor sets `supportsCompaction`; Kiro compacts through its own request instead.
+  const compactsThroughPrompt = runtime.driver === "grok";
+  // Like the adapter: notes go out until a prompt carrying that text succeeds, and a new runtime
+  // or compaction resets that. Not mirrored, as no recording has them: Copilot compaction events,
+  // child-session compactions, and ACP v2 prompts that settle through an idle `state_update`.
+  const deliveredNotes = new Map<unknown, string>();
+  // A prompt's success records delivery only if no compaction completed after it was sent.
+  const compactionCounts = new Map<unknown, number>();
+  const completedCompactionIds = new Set<string>();
+  // A turn that completes with a compaction still open projects it as completed.
+  const openCompactions = new Map<unknown, Set<unknown>>();
+  const markCompacted = (sessionId: unknown, compactionId?: unknown) => {
+    if (typeof compactionId === "string") {
+      const key = `${String(sessionId)}\u0000${compactionId}`;
+      if (completedCompactionIds.has(key)) return;
+      completedCompactionIds.add(key);
+    }
+    deliveredNotes.delete(sessionId);
+    compactionCounts.set(sessionId, (compactionCounts.get(sessionId) ?? 0) + 1);
+  };
+  let pendingPrompt:
+    | {
+        readonly sessionId: unknown;
+        /** The runtime notes the prompt carried, if any. */
+        readonly notes: string | undefined;
+        readonly compact: boolean;
+        readonly compactionsAtSend: number;
+      }
+    | undefined;
+  let pendingKiroCompact: { readonly sessionId: unknown } | undefined;
 
   return {
     ...transcript,
     entries: transcript.entries.map((entry) => {
+      if (entry.type === "emit_inbound") {
+        const frame = asFrame(entry.frame);
+        if (frame?.kind === "response" && frame.method === "session/prompt" && pendingPrompt) {
+          const stopReason = isRecord(frame.result) ? frame.result.stopReason : undefined;
+          const delivered =
+            frame.error === undefined &&
+            stopReason !== "cancelled" &&
+            stopReason !== "refusal" &&
+            stopReason !== "error";
+          const open = openCompactions.get(pendingPrompt.sessionId);
+          if (delivered && open !== undefined && open.size > 0) {
+            openCompactions.delete(pendingPrompt.sessionId);
+            markCompacted(pendingPrompt.sessionId);
+          }
+          if (delivered && pendingPrompt.compact) {
+            markCompacted(pendingPrompt.sessionId);
+          } else if (
+            delivered &&
+            pendingPrompt.notes !== undefined &&
+            (compactionCounts.get(pendingPrompt.sessionId) ?? 0) === pendingPrompt.compactionsAtSend
+          ) {
+            deliveredNotes.set(pendingPrompt.sessionId, pendingPrompt.notes);
+          }
+          pendingPrompt = undefined;
+        }
+        if (
+          frame?.kind === "response" &&
+          frame.method === "_kiro/session/compact" &&
+          pendingKiroCompact
+        ) {
+          // Kiro's adapter accepts only `{ success: true }`.
+          if (isRecord(frame.result) && frame.result.success === true) {
+            markCompacted(pendingKiroCompact.sessionId);
+          }
+          pendingKiroCompact = undefined;
+        }
+        const update =
+          frame?.method === "session/update" && isRecord(frame.params)
+            ? frame.params.update
+            : undefined;
+        if (
+          isRecord(update) &&
+          update.sessionUpdate === "compaction_update" &&
+          isRecord(frame?.params)
+        ) {
+          const sessionId = frame.params.sessionId;
+          const open = openCompactions.get(sessionId) ?? new Set<unknown>();
+          if (update.status === "in_progress") {
+            openCompactions.set(sessionId, open.add(update.compactionId));
+          } else {
+            open.delete(update.compactionId);
+          }
+          if (update.status === "completed") markCompacted(sessionId, update.compactionId);
+        }
+        return entry;
+      }
       if (entry.type !== "expect_outbound") return entry;
       const frame = entry.frame;
       if (typeof frame !== "object" || frame === null) return entry;
@@ -38,6 +130,43 @@ export function materializeReplayTranscriptRuntimeInstructions(
           ? entry
           : { ...entry, frame: { ...frame, message: `${frame.message}\n\n${instructions}` } };
       }
+      if (
+        "method" in frame &&
+        (frame.method === "session/close" || frame.method === "initialize")
+      ) {
+        // A closed or restarted session comes back in a new runtime, which resends the instructions.
+        deliveredNotes.clear();
+        completedCompactionIds.clear();
+        openCompactions.clear();
+        pendingPrompt = undefined;
+        pendingKiroCompact = undefined;
+        return entry;
+      }
+      const params = "params" in frame && isRecord(frame.params) ? frame.params : undefined;
+      const selectedModel =
+        "method" in frame && frame.method === "session/set_config_option"
+          ? params?.configId === "model"
+            ? params.value
+            : undefined
+          : "method" in frame && frame.method === "session/set_model"
+            ? params?.modelId
+            : undefined;
+      if (typeof selectedModel === "string") {
+        sessionModels.set(params?.sessionId, selectedModel);
+        return entry;
+      }
+      if (
+        "method" in frame &&
+        frame.method === "_kiro/session/compact" &&
+        "params" in frame &&
+        typeof frame.params === "object" &&
+        frame.params !== null &&
+        "sessionId" in frame.params
+      ) {
+        // Once it succeeds, Kiro's native compaction makes the next prompt resend them.
+        pendingKiroCompact = { sessionId: frame.params.sessionId };
+        return entry;
+      }
       if (
         "method" in frame &&
         frame.method === "session/prompt" &&
@@ -47,30 +176,75 @@ export function materializeReplayTranscriptRuntimeInstructions(
         "prompt" in frame.params &&
         Array.isArray(frame.params.prompt)
       ) {
+        const promptSessionId = "sessionId" in frame.params ? frame.params.sessionId : undefined;
         const prompt: ReadonlyArray<unknown> = frame.params.prompt;
-        const lastPart = prompt.at(-1);
-        if (
-          typeof lastPart === "object" &&
-          lastPart !== null &&
-          "type" in lastPart &&
-          lastPart.type === "text" &&
-          "text" in lastPart &&
-          typeof lastPart.text === "string" &&
-          // A recording that switched models mid-thread already carries the
-          // instructions for the model each prompt ran on.
-          (lastPart.text === instructions || lastPart.text.startsWith("<runtime_info>"))
-        ) {
+        const firstText = promptPartText(prompt[0])?.trim();
+        // Like the adapter, native slash commands go out without instructions. Where the agent
+        // compacts through the prompt, a successful `/compact` makes the next prompt resend them.
+        if (firstText?.startsWith("/") === true) {
+          pendingPrompt = {
+            sessionId: promptSessionId,
+            notes: undefined,
+            compact:
+              compactsThroughPrompt && prompt.length === 1 && /^\/compact(?:\s|$)/.test(firstText),
+            compactionsAtSend: compactionCounts.get(promptSessionId) ?? 0,
+          };
           return entry;
         }
+        const lastText = promptPartText(prompt.at(-1));
+        const expected = notesFor(promptSessionId);
+        // A recording that switched models mid-thread already carries the
+        // instructions for the model each prompt ran on.
+        const recordedNotes =
+          lastText === expected || lastText?.startsWith("<runtime_info>") === true
+            ? lastText
+            : undefined;
+        const resend =
+          recordedNotes === undefined && deliveredNotes.get(promptSessionId) !== expected;
+        pendingPrompt = {
+          sessionId: promptSessionId,
+          // Recorders normalize the notes they keep, so a recorded block stands for this model's.
+          notes: recordedNotes !== undefined || resend ? expected : undefined,
+          compact: false,
+          compactionsAtSend: compactionCounts.get(promptSessionId) ?? 0,
+        };
+        if (!resend) return entry;
         return {
           ...entry,
           frame: {
             ...frame,
-            params: { ...frame.params, prompt: [...prompt, { type: "text", text: instructions }] },
+            params: { ...frame.params, prompt: [...prompt, { type: "text", text: expected }] },
           },
         };
       }
       return entry;
     }),
   };
 }
+
+function promptPartText(part: unknown): string | undefined {
+  return typeof part === "object" &&
+    part !== null &&
+    "type" in part &&
+    part.type === "text" &&
+    "text" in part &&
+    typeof part.text === "string"
+    ? part.text
+    : undefined;
+}
+
+type ReplayFrame = {
+  readonly kind?: unknown;
+  readonly method?: unknown;
+  readonly params?: unknown;
+  readonly result?: unknown;
+  readonly error?: unknown;
+};
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === "object" && value !== null;
+}
+
+function asFrame(value: unknown): ReplayFrame | undefined {
+  return isRecord(value) ? value : undefined;
+}