fix(prompts): dynamically list active tools in Plan Mode system prompt

- Updates `PromptProvider` to retrieve and alphabetically sort the active tools from `ToolRegistry` for the Plan Mode prompt list.
- Removes hardcoded descriptions for `write_file` and `replace` from `snippets.ts` and `snippets.legacy.ts` as they are now dynamically included.
- Modifies verbiage in Plan Mode instructions to reflect that tools may not be exclusively "read-only" when workspace policies apply overrides.
- Updates snapshot assertions and prompt test mocks to verify the correct dynamic and sorted injection of tool descriptions.

packages/core/src/core/__snapshots__/prompts.test.ts.snap

@@ -42,11 +42,9 @@ For example:
 You are operating in **Plan Mode** - a structured planning workflow for designing implementation strategies before execution.
 
 ## Available Tools
-The following read-only tools are available in Plan Mode:
+The following tools are available in Plan Mode:
   <tool>\`glob\`</tool>
   <tool>\`grep_search\`</tool>
-- \`write_file\` - Save plans to the plans directory (see Plan Storage below)
-- \`replace\` - Update plans in the plans directory
 
 ## Plan Storage
 - Save your plans as Markdown (.md) files ONLY within: \`/tmp/plans/\`
@@ -174,11 +172,9 @@ For example:
 You are operating in **Plan Mode** - a structured planning workflow for designing implementation strategies before execution.
 
 ## Available Tools
-The following read-only tools are available in Plan Mode:
+The following tools are available in Plan Mode:
   <tool>\`glob\`</tool>
   <tool>\`grep_search\`</tool>
-- \`write_file\` - Save plans to the plans directory (see Plan Storage below)
-- \`replace\` - Update plans in the plans directory
 
 ## Plan Storage
 - Save your plans as Markdown (.md) files ONLY within: \`/tmp/plans/\`
@@ -424,11 +420,9 @@ For example:
 You are operating in **Plan Mode** - a structured planning workflow for designing implementation strategies before execution.
 
 ## Available Tools
-The following read-only tools are available in Plan Mode:
+The following tools are available in Plan Mode:
   <tool>\`glob\`</tool>
   <tool>\`grep_search\`</tool>
-- \`write_file\` - Save plans to the plans directory (see Plan Storage below)
-- \`replace\` - Update plans in the plans directory
 
 ## Plan Storage
 - Save your plans as Markdown (.md) files ONLY within: \`/tmp/project-temp/plans/\`

packages/core/src/core/prompts.test.ts

@@ -25,6 +25,7 @@ import {
 } from '../config/models.js';
 import { ApprovalMode } from '../policy/types.js';
 import { DiscoveredMCPTool } from '../tools/mcp-tool.js';
+import type { AnyDeclarativeTool } from '../tools/tool-registry.js';
 import type { CallableTool } from '@google/genai';
 import type { MessageBus } from '../confirmation-bus/message-bus.js';
 
@@ -85,6 +86,12 @@ describe('Core System Prompt (prompts.ts)', () => {
       getToolRegistry: vi.fn().mockReturnValue({
         getAllToolNames: vi.fn().mockReturnValue(['grep_search', 'glob']),
         getAllTools: vi.fn().mockReturnValue([]),
+        getActiveTools: vi
+          .fn()
+          .mockReturnValue([
+            { name: 'grep_search' } as unknown as AnyDeclarativeTool,
+            { name: 'glob' } as unknown as AnyDeclarativeTool,
+          ]),
       }),
       getEnableShellOutputEfficiency: vi.fn().mockReturnValue(true),
       storage: {
@@ -452,24 +459,11 @@ describe('Core System Prompt (prompts.ts)', () => {
         true, // isReadOnly
       );
 
-      const nonReadOnlyMcpTool = new DiscoveredMCPTool(
-        {} as CallableTool,
-        'nonreadonly-server',
-        'non_read_static_value',
-        'A non-read-only tool',
-        {},
-        {} as MessageBus,
-        false,
-        false,
-      );
+      // Note: non-read-only MCP tools are implicitly filtered out by the logic
+      // because they are not potentially allowed in Plan Mode by default.
 
-      vi.mocked(mockConfig.getToolRegistry().getAllTools).mockReturnValue([
+      vi.mocked(mockConfig.getToolRegistry().getActiveTools).mockReturnValue([
         readOnlyMcpTool,
-        nonReadOnlyMcpTool,
-      ]);
-      vi.mocked(mockConfig.getToolRegistry().getAllToolNames).mockReturnValue([
-        readOnlyMcpTool.name,
-        nonReadOnlyMcpTool.name,
       ]);
 
       const prompt = getCoreSystemPrompt(mockConfig);
@@ -483,10 +477,10 @@ describe('Core System Prompt (prompts.ts)', () => {
     it('should only list available tools in PLAN mode', () => {
       vi.mocked(mockConfig.getApprovalMode).mockReturnValue(ApprovalMode.PLAN);
       // Only enable a subset of tools, including ask_user
-      vi.mocked(mockConfig.getToolRegistry().getAllToolNames).mockReturnValue([
-        'glob',
-        'read_file',
-        'ask_user',
+      vi.mocked(mockConfig.getToolRegistry().getActiveTools).mockReturnValue([
+        { name: 'glob' } as unknown as AnyDeclarativeTool,
+        { name: 'read_file' } as unknown as AnyDeclarativeTool,
+        { name: 'ask_user' } as unknown as AnyDeclarativeTool,
       ]);
 
       const prompt = getCoreSystemPrompt(mockConfig);

packages/core/src/prompts/promptProvider.ts

@@ -22,7 +22,6 @@ import {
 import { CodebaseInvestigatorAgent } from '../agents/codebase-investigator.js';
 import { isGitRepository } from '../utils/gitUtils.js';
 import {
-  PLAN_MODE_TOOLS,
   WRITE_TODOS_TOOL_NAME,
   READ_FILE_TOOL_NAME,
   ENTER_PLAN_MODE_TOOL_NAME,
@@ -67,25 +66,17 @@ export class PromptProvider {
     const contextFilenames = getAllGeminiMdFilenames();
 
     // --- Context Gathering ---
-    let planModeToolsList = PLAN_MODE_TOOLS.filter((t) =>
-      enabledToolNames.has(t),
-    )
-      .map((t) => `  <tool>\`${t}\`</tool>`)
-      .join('\n');
-
-    // Add read-only MCP tools to the list
+    let planModeToolsList = '';
     if (isPlanMode) {
-      const allTools = config.getToolRegistry().getAllTools();
-      const readOnlyMcpTools = allTools.filter(
-        (t): t is DiscoveredMCPTool =>
-          t instanceof DiscoveredMCPTool && !!t.isReadOnly,
-      );
-      if (readOnlyMcpTools.length > 0) {
-        const mcpToolsList = readOnlyMcpTools
-          .map((t) => `  <tool>\`${t.name}\` (${t.serverName})</tool>`)
-          .join('\n');
-        planModeToolsList += `\n${mcpToolsList}`;
-      }
+      const activeTools = config.getToolRegistry().getActiveTools();
+      activeTools.sort((a, b) => a.name.localeCompare(b.name));
+      planModeToolsList = activeTools
+        .map((t) => {
+          const serverSuffix =
+            t instanceof DiscoveredMCPTool ? ` (${t.serverName})` : '';
+          return `  <tool>\`${t.name}\`${serverSuffix}</tool>`;
+        })
+        .join('\n');
     }
 
     let basePrompt: string;

packages/core/src/prompts/snippets.legacy.ts

@@ -398,10 +398,8 @@ export function renderPlanningWorkflow(
 You are operating in **Plan Mode** - a structured planning workflow for designing implementation strategies before execution.
 
 ## Available Tools
-The following read-only tools are available in Plan Mode:
+The following tools are available in Plan Mode:
 ${options.planModeToolsList}
-- \`${WRITE_FILE_TOOL_NAME}\` - Save plans to the plans directory (see Plan Storage below)
-- \`${EDIT_TOOL_NAME}\` - Update plans in the plans directory
 
 ## Plan Storage
 - Save your plans as Markdown (.md) files ONLY within: \`${options.plansDir}/\`

packages/core/src/prompts/snippets.ts

@@ -452,11 +452,9 @@ export function renderPlanningWorkflow(
 You are operating in **Plan Mode**. Your goal is to produce a detailed implementation plan in \`${options.plansDir}/\` and get user approval before editing source code.
 
 ## Available Tools
-The following read-only tools are available in Plan Mode:
+The following tools are available in Plan Mode:
 <available_tools>
 ${options.planModeToolsList}
-  <tool>${formatToolName(WRITE_FILE_TOOL_NAME)} - Save plans to the plans directory</tool>
-  <tool>${formatToolName(EDIT_TOOL_NAME)} - Update plans in the plans directory</tool>
 </available_tools>
 
 ## Rules