diff --git a/packages/core/src/core/geminiChat.ts b/packages/core/src/core/geminiChat.ts
index 319f994ba0..411c9a2724 100644
--- a/packages/core/src/core/geminiChat.ts
+++ b/packages/core/src/core/geminiChat.ts
@@ -41,6 +41,7 @@ import {
   logContentRetry,
   logContentRetryFailure,
 } from '../telemetry/loggers.js';
+import { clearDetailedSpanState } from '../telemetry/detailed-span-attributes.js';
 import { type ChatRecordingService } from '../services/chatRecordingService.js';
 import {
   ChatCompressionService,
@@ -1400,6 +1401,7 @@ export class GeminiChat {
       this.setHistory(newHistory);
       debugLogger.debug('[FILE_READ_CACHE] clear after auto tryCompress');
       this.config.getFileReadCache().clear();
+      clearDetailedSpanState();
       this.lastPromptTokenCount = info.newTokenCount;
       this.telemetryService?.setLastPromptTokenCount(info.newTokenCount);
       // Reset the consecutive-failure counter on success so a forced /compress
diff --git a/packages/core/src/telemetry/detailed-span-attributes.test.ts b/packages/core/src/telemetry/detailed-span-attributes.test.ts
index 918e8d2a2b..a0ee1bb217 100644
--- a/packages/core/src/telemetry/detailed-span-attributes.test.ts
+++ b/packages/core/src/telemetry/detailed-span-attributes.test.ts
@@ -400,5 +400,28 @@ describe('detailed-span-attributes', () => {
       addSystemPromptAttributes(config, span2, 'Same prompt');
       expect(span2.attrs['system_prompt']).toBe('Same prompt');
     });
+
+    it('resets seenHashes so tool schema full body is re-emitted after compression', () => {
+      const config = createMockConfig();
+      const tools = [
+        { name: 'Read', description: 'Read a file', parameters: {} },
+      ];
+
+      const span1 = createMockSpan();
+      addToolSchemaAttributes(config, span1, tools);
+      expect(span1.events.length).toBe(1);
+      expect(span1.events[0]!.attributes['tool_definition']).toBeDefined();
+
+      const span2 = createMockSpan();
+      addToolSchemaAttributes(config, span2, tools);
+      expect(span2.events.length).toBe(0);
+
+      clearDetailedSpanState();
+
+      const span3 = createMockSpan();
+      addToolSchemaAttributes(config, span3, tools);
+      expect(span3.events.length).toBe(1);
+      expect(span3.events[0]!.attributes['tool_definition']).toBeDefined();
+    });
   });
 });
diff --git a/packages/core/src/telemetry/detailed-span-attributes.ts b/packages/core/src/telemetry/detailed-span-attributes.ts
index e38c57e819..cf1db36547 100644
--- a/packages/core/src/telemetry/detailed-span-attributes.ts
+++ b/packages/core/src/telemetry/detailed-span-attributes.ts
@@ -13,8 +13,8 @@ import { safeJsonStringify } from '../utils/safeJsonStringify.js';
 const MAX_CONTENT_SIZE = 60 * 1024; // 60KB
 const SYSTEM_PROMPT_PREVIEW_LENGTH = 500;
 
-// Process-global; intentionally never cleared in production. Bounded by the
-// number of unique system prompts + tool schemas seen in one session.
+// Process-global dedup set. Cleared on chat compression so post-compaction
+// spans re-emit full system prompts and tool schemas.
 const seenHashes = new Set<string>();
 
 function isEnabled(config: Config): boolean {
diff --git a/packages/core/src/telemetry/index.ts b/packages/core/src/telemetry/index.ts
index 6ad5cb13c3..cd8aad316b 100644
--- a/packages/core/src/telemetry/index.ts
+++ b/packages/core/src/telemetry/index.ts
@@ -172,4 +172,5 @@ export {
   addToolInputAttributes,
   addToolResultAttributes,
   truncateContent,
+  clearDetailedSpanState,
 } from './detailed-span-attributes.js';