Merge pull request #1956 from codeg-dev/fix/prometheus-table-restoration-and-cancel-consistency

fix(agents): replace background_cancel(all=true) with individual task cancellation

src/agents/hephaestus.ts

@@ -292,7 +292,8 @@ Prompt structure for each agent:
 - NEVER use \`run_in_background=false\` for explore/librarian
 - Continue your work immediately after launching background agents
 - Collect results with \`background_output(task_id="...")\` when needed
-- BEFORE final answer: \`background_cancel(all=true)\` to clean up
+- BEFORE final answer, cancel DISPOSABLE tasks individually: \`background_cancel(taskId="bg_explore_xxx")\`, \`background_cancel(taskId="bg_librarian_xxx")\`
+- **NEVER use \`background_cancel(all=true)\`** — it kills tasks whose results you haven't collected yet
 
 ### Search Stop Conditions