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Preserve user guidance through history compression, stabilize Flash index targets, and retire withdrawn checks without applying stale verdicts.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

@@ -1070,13 +1070,14 @@ limitations under the License.
                                 <!-- Generic Tool Calls (Text format for note tools, video analyzer, and other sub-agents) -->
                                 @if (shouldShowTool(item.data, block.data) && !isDeviceActionTool(item.data)) {
                                   <div class="step-generic-tool"
-                                    [class.is-running]="isItemRunning(item, block)"
+                                    [class.is-running]="isToolLineRunning(item, block)"
                                     [class.is-note-tool]="isNoteTool(item.data)"
                                     [class.is-video-tool]="isVideoTool(item.data)"
                                     [class.is-video-attention]="isVideoTool(item.data) && isVideoAnalysisAttention(item.data)"
+                                    [attr.title]="getCompressionPhaseTitle(item.data)"
                                     >
                                     <div class="tool-call-label">
-                                      <span class="stream-status-dot" [class.streaming]="isItemRunning(item, block)"></span>
+                                      <span class="stream-status-dot" [class.streaming]="isToolLineRunning(item, block)"></span>
                                       <div class="tool-call-text">
                                         <span>{{ isVideoTool(item.data) ? getVideoAnalysisLabel(item.data) : getToolDisplayLabel(item.data) }}{{ ((isNoteTool(item.data) && getToolKey(item.data)) || isVideoTool(item.data)) ? ':' : '' }}</span>
                                         <!-- Note Tool Pill -->