fix(cli): make impact [target] optional so --uid resolves alone (U1, #1907)

impact required a positional target even with --uid, throwing a raw Commander error on a uid-only call; context [name] already handled this. Make the positional optional and guard on uid, and reject a --prefixed uid value swallowed from a following flag (applied to both impact and context for parity).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gitnexus/src/cli/index.ts

@@ -219,7 +219,7 @@ program
   .action(createLbugLazyAction(() => import('./tool.js'), 'contextCommand'));
 
 program
-  .command('impact <target>')
+  .command('impact [target]')
   .description('Blast radius analysis: what breaks if you change a symbol')
   .option('-d, --direction <dir>', 'upstream (dependants) or downstream (dependencies)', 'upstream')
   .option('-r, --repo <name>', 'Target repository')

gitnexus/src/cli/tool.ts

@@ -94,6 +94,11 @@ export async function contextCommand(
     content?: boolean;
   },
 ): Promise<void> {
+  // Reject a `--`-prefixed uid swallowed from a following flag (see impactCommand).
+  if (options?.uid?.startsWith('--')) {
+    cliErrorKey('tool.usage.context');
+    process.exit(1);
+  }
   if (!name?.trim() && !options?.uid) {
     cliErrorKey('tool.usage.context');
     process.exit(1);
@@ -111,7 +116,7 @@ export async function contextCommand(
 }
 
 export async function impactCommand(
-  target: string,
+  target?: string,
   options?: {
     direction?: string;
     repo?: string;
@@ -125,7 +130,16 @@ export async function impactCommand(
     summaryOnly?: boolean;
   },
 ): Promise<void> {
-  if (!target?.trim()) {
+  // A `--`-prefixed uid means Commander swallowed a following flag as the uid
+  // value (e.g. `impact --uid --file x` → uid === '--file'). Reject it rather
+  // than forwarding a garbage uid that would silently resolve to not-found.
+  if (options?.uid?.startsWith('--')) {
+    cliErrorKey('tool.usage.impact');
+    process.exit(1);
+  }
+  // Target is an optional positional: a uid alone is enough to resolve (parity
+  // with `context [name]`). Only error when neither a target nor a uid is given.
+  if (!target?.trim() && !options?.uid) {
     cliErrorKey('tool.usage.impact');
     process.exit(1);
   }
@@ -137,7 +151,7 @@ export async function impactCommand(
     const parsedLimit = Number.isFinite(rawLimit) ? rawLimit : undefined;
     const parsedOffset = Number.isFinite(rawOffset) ? rawOffset : undefined;
     const result = await backend.callTool('impact', {
-      target,
+      target: target || undefined,
       target_uid: options?.uid,
       file_path: options?.file,
       kind: options?.kind,

gitnexus/test/unit/cli-impact-disambiguation.test.ts

@@ -72,4 +72,41 @@ describe('CLI impact disambiguation flags (#1907)', () => {
     expect(params.file_path).toBeUndefined();
     expect(params.kind).toBeUndefined();
   });
+
+  // U1 (#1914 review F1): impact's positional target is now optional, so a uid
+  // alone resolves — parity with `context [name]`.
+  it('resolves uid-only with no positional target (parity with context)', async () => {
+    await impactCommand(undefined, {
+      direction: 'upstream',
+      uid: 'Function:src/auth.ts:login',
+    });
+
+    expect(callTool).toHaveBeenCalledTimes(1);
+    const params = callTool.mock.calls[0][1] as Record<string, unknown>;
+    expect(params.target_uid).toBe('Function:src/auth.ts:login');
+    expect(params.target).toBeUndefined();
+  });
+
+  it('errors when neither a target nor a uid is provided', async () => {
+    const exitSpy = vi.spyOn(process, 'exit').mockImplementation((() => {
+      throw new Error('process.exit');
+    }) as never);
+
+    await expect(impactCommand(undefined, {})).rejects.toThrow('process.exit');
+    expect(exitSpy).toHaveBeenCalledWith(1);
+    expect(callTool).not.toHaveBeenCalled();
+
+    exitSpy.mockRestore();
+  });
+
+  it('rejects a --prefixed uid value (a flag swallowed by Commander) without forwarding it', async () => {
+    const exitSpy = vi.spyOn(process, 'exit').mockImplementation((() => {
+      throw new Error('process.exit');
+    }) as never);
+
+    await expect(impactCommand(undefined, { uid: '--file' })).rejects.toThrow('process.exit');
+    expect(callTool).not.toHaveBeenCalled();
+
+    exitSpy.mockRestore();
+  });
 });