refactor: unify agent history and harden runtime diagnostics

Preserve user guidance through history compression, stabilize Flash index targets, and retire withdrawn checks without applying stale verdicts.

Improve runtime diagnostics, tool responses, and history rendering. Simplify documentation and comments.

Validation: 2076 tests passed in the full suite; 381 affected tests and 26 frontend tests passed after cleanup. Ruff and the quality ratchet passed.

apps/showcase_ui/src/app/components/agent-stream/agent-stream.component.ts

@@ -172,6 +172,9 @@ import {
   getUniqueGenericTools,
   getToolKey,
   getToolDisplayLabel,
+  isCompressionTool,
+  isCompressionWaiting,
+  getCompressionPhaseLabel,
   getToolIcon,
   getToolTitle,
   getToolTargetText,
@@ -1465,6 +1468,20 @@ export class AgentStreamComponent implements AfterViewInit {
     return getToolDisplayLabel(tool, this.isFirstSaveNoteForKey(tool));
   }
 
+  /** Short plain-language phase for a compress_history line (hover title). */
+  public getCompressionPhaseTitle(tool: any): string | null {
+    return isCompressionTool(tool) ? getCompressionPhaseLabel(tool) : null;
+  }
+
+  /**
+   * A generic tool line pulses only while work is in flight. A compression
+   * whose summary is ready but held back by the context gate is waiting, not
+   * running, even though its trace status is still `running`.
+   */
+  public isToolLineRunning(item: any, block: any): boolean {
+    return this.isItemRunning(item, block) && !isCompressionWaiting(item?.data);
+  }
+
   public isNoteTool(tool: any): boolean {
     return isNoteTool(tool);
   }