diff --git a/packages/coding-agent/CHANGELOG.md b/packages/coding-agent/CHANGELOG.md
index 318437c8..491b4b58 100644
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Fixed
 
+- Fixed `tool_result` / `afterToolCall` extension handling for error results by forwarding `details` and `isError` overrides through `AgentSession` instead of dropping them when `isError` was already true ([#3051](https://github.com/badlogic/pi-mono/issues/3051))
 - Fixed missing root exports for `RpcClient` and RPC protocol types from `@mariozechner/pi-coding-agent`, so ESM consumers can import them from the main package entrypoint ([#3275](https://github.com/badlogic/pi-mono/issues/3275))
 - Fixed Bun binary asset path resolution to honor `PI_PACKAGE_DIR` for built-in themes, HTML export templates, and interactive bundled assets ([#3074](https://github.com/badlogic/pi-mono/issues/3074))
 - Fixed user-message turn spacing in interactive mode by restoring an inter-message spacer before user turns (except the first user message), preventing assistant and user blocks from rendering flush together.
diff --git a/packages/coding-agent/src/core/agent-session.ts b/packages/coding-agent/src/core/agent-session.ts
index bccc5b8a..4f8bbfd7 100644
--- a/packages/coding-agent/src/core/agent-session.ts
+++ b/packages/coding-agent/src/core/agent-session.ts
@@ -398,17 +398,18 @@ export class AgentSession {
 				toolCallId: toolCall.id,
 				input: args as Record<string, unknown>,
 				content: result.content,
-				details: isError ? undefined : result.details,
+				details: result.details,
 				isError,
 			});
 
-			if (!hookResult || isError) {
+			if (!hookResult) {
 				return undefined;
 			}
 
 			return {
 				content: hookResult.content,
 				details: hookResult.details,
+				isError: hookResult.isError ?? isError,
 			};
 		};
 	}