feat(ui): redesign context and compression UI for a more seamless experience

- Added ui.showContextWindowWarning setting (default false).
- Implemented forced auto-compression on context overflow when warning is disabled.
- Redesigned compression messages to be subtle (gray, no icon, left border).
- Removed automatic context usage percentage from the minimal/focus UI.
- Changed ui.hideContextSummary default to true.
- Updated and verified all relevant tests.

Note: Includes a behavioral change where the CLI now attempts to force-compress
history when the context window is full rather than blocking by default.

packages/core/src/config/config.ts

@@ -673,6 +673,7 @@ export interface ConfigParameters {
     agents?: AgentSettings;
   }>;
   enableConseca?: boolean;
+  showContextWindowWarning?: boolean;
   billing?: {
     overageStrategy?: OverageStrategy;
   };
@@ -708,6 +709,7 @@ export class Config implements McpContext, AgentLoopContext {
   private readonly question: string | undefined;
   private readonly worktreeSettings: WorktreeSettings | undefined;
   readonly enableConseca: boolean;
+  private readonly showContextWindowWarning: boolean;
 
   private readonly coreTools: string[] | undefined;
   private readonly mainAgentTools: string[] | undefined;
@@ -1146,6 +1148,7 @@ export class Config implements McpContext, AgentLoopContext {
     this.fileExclusions = new FileExclusions(this);
     this.eventEmitter = params.eventEmitter;
     this.enableConseca = params.enableConseca ?? false;
+    this.showContextWindowWarning = params.showContextWindowWarning ?? false;
 
     // Initialize Safety Infrastructure
     const contextBuilder = new ContextBuilder(this);
@@ -2053,6 +2056,10 @@ export class Config implements McpContext, AgentLoopContext {
     return this.mcpEnabled;
   }
 
+  getShowContextWindowWarning(): boolean {
+    return this.showContextWindowWarning;
+  }
+
   getMcpEnablementCallbacks(): McpEnablementCallbacks | undefined {
     return this.mcpEnablementCallbacks;
   }

packages/core/src/core/client.ts

@@ -614,7 +614,7 @@ export class GeminiClient {
       yield { type: GeminiEventType.ChatCompressed, value: compressed };
     }
 
-    const remainingTokenCount =
+    let remainingTokenCount =
       tokenLimit(modelForLimitCheck) - this.getChat().getLastPromptTokenCount();
 
     await this.tryMaskToolOutputs(this.getHistory());
@@ -628,11 +628,28 @@ export class GeminiClient {
     );
 
     if (estimatedRequestTokenCount > remainingTokenCount) {
-      yield {
-        type: GeminiEventType.ContextWindowWillOverflow,
-        value: { estimatedRequestTokenCount, remainingTokenCount },
-      };
-      return turn;
+      if (!this.config.getShowContextWindowWarning()) {
+        const forcedCompressed = await this.tryCompressChat(prompt_id, true);
+        if (
+          forcedCompressed.compressionStatus === CompressionStatus.COMPRESSED
+        ) {
+          yield {
+            type: GeminiEventType.ChatCompressed,
+            value: forcedCompressed,
+          };
+          remainingTokenCount =
+            tokenLimit(modelForLimitCheck) -
+            this.getChat().getLastPromptTokenCount();
+        }
+      }
+
+      if (estimatedRequestTokenCount > remainingTokenCount) {
+        yield {
+          type: GeminiEventType.ContextWindowWillOverflow,
+          value: { estimatedRequestTokenCount, remainingTokenCount },
+        };
+        return turn;
+      }
     }
 
     // Prevent context updates from being sent while a tool call is