merge(read-exp): Reconcile 'afw/read-exp-v3' with 'main'

- Integrate model-specific tool optimizations (isGemini3) into read-file and snippets.
- Reconcile prompt snippets with main's Context Efficiency mandates and experiment's discovery guidelines.
- Adopt main's refactored tool definition structure while retaining experiment's surgical extraction guidance.
- Resolve pagination and truncation logic in file utilities.
- Update snapshots and verify with full test suite.
- Align prompt provider and snippets with main's code style and linting patterns.

packages/core/src/prompts/promptProvider.ts

@@ -119,6 +119,7 @@ export class PromptProvider {
         })),
         coreMandates: this.withSection('coreMandates', () => ({
           interactive: interactiveMode,
+          isGemini3: isModernModel,
           hasSkills: skills.length > 0,
           hasHierarchicalMemory,
           contextFilenames,
@@ -175,7 +176,6 @@ export class PromptProvider {
           'operationalGuidelines',
           () => ({
             interactive: interactiveMode,
-            isGemini3: isModernModel,
             enableShellEfficiency: config.getEnableShellOutputEfficiency(),
             interactiveShellEnabled: config.isInteractiveShellEnabled(),
           }),
@@ -196,9 +196,13 @@ export class PromptProvider {
           : this.withSection('finalReminder', () => ({
               readFileToolName: READ_FILE_TOOL_NAME,
             })),
-      };
+      } as snippets.SystemPromptOptions;
 
-      basePrompt = activeSnippets.getCoreSystemPrompt(options);
+      // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
+      const getCoreSystemPrompt = activeSnippets.getCoreSystemPrompt as (
+        options: snippets.SystemPromptOptions,
+      ) => string;
+      basePrompt = getCoreSystemPrompt(options);
     }
 
     // --- Finalization (Shell) ---

packages/core/src/prompts/snippets.ts

@@ -35,6 +35,7 @@ export interface SystemPromptOptions {
   sandbox?: SandboxMode;
   interactiveYoloMode?: boolean;
   gitRepo?: GitRepoOptions;
+  finalReminder?: FinalReminderOptions;
 }
 
 export interface PreambleOptions {
@@ -60,7 +61,6 @@ export interface PrimaryWorkflowsOptions {
 
 export interface OperationalGuidelinesOptions {
   interactive: boolean;
-  isGemini3: boolean;
   enableShellEfficiency: boolean;
   interactiveShellEnabled: boolean;
 }
@@ -71,6 +71,10 @@ export interface GitRepoOptions {
   interactive: boolean;
 }
 
+export interface FinalReminderOptions {
+  readFileToolName: string;
+}
+
 export interface PlanningWorkflowOptions {
   planModeToolsList: string;
   plansDir: string;