🤖 fix: omit providerMetadata from compaction summary to fix context display

The compaction API response's providerMetadata contains cacheCreationInputTokens
from the pre-compaction context, which inflates the context usage display until
the next message is sent. By omitting providerMetadata from the summary message,
context usage correctly shows just the compaction output tokens.

The historicalUsage field still preserves full cost accounting from pre-compaction
messages.

_Generated with mux_

Author: ethanndickson

src/node/services/compactionHandler.test.ts

@@ -255,7 +255,7 @@ describe("CompactionHandler", () => {
         model: "claude-3-5-sonnet-20241022",
         usage,
         duration: 2000,
-        providerMetadata: { foo: "bar" },
+        providerMetadata: { anthropic: { cacheCreationInputTokens: 50000 } },
         systemMessageTokens: 100,
       });
       await handler.handleCompletion(event);
@@ -266,14 +266,15 @@ describe("CompactionHandler", () => {
       });
       expect(summaryEvent).toBeDefined();
       const sevt = summaryEvent?.data.message as MuxMessage;
+      // providerMetadata is omitted to avoid inflating context with pre-compaction cacheCreationInputTokens
       expect(sevt.metadata).toMatchObject({
         model: "claude-3-5-sonnet-20241022",
         usage,
         duration: 2000,
-        providerMetadata: { foo: "bar" },
         systemMessageTokens: 100,
         compacted: true,
       });
+      expect(sevt.metadata?.providerMetadata).toBeUndefined();
     });
 
     it("should emit stream-end event to frontend", async () => {

src/node/services/compactionHandler.ts

@@ -112,7 +112,10 @@ export class CompactionHandler {
     }
     const deletedSequences = clearResult.data;
 
-    // Create summary message with metadata
+    // Create summary message with metadata.
+    // We omit providerMetadata because it contains cacheCreationInputTokens from the
+    // pre-compaction context, which inflates context usage display. The historicalUsage
+    // field preserves full cost accounting from pre-compaction messages.
     const summaryMessage = createMuxMessage(
       `summary-${Date.now()}-${Math.random().toString(36).substring(2, 11)}`,
       "assistant",
@@ -123,7 +126,6 @@ export class CompactionHandler {
         model: metadata.model,
         usage: metadata.usage,
         historicalUsage,
-        providerMetadata: metadata.providerMetadata,
         duration: metadata.duration,
         systemMessageTokens: metadata.systemMessageTokens,
         muxMetadata: { type: "normal" },