fix(tui): address PR review feedback

Fixes from OutThisLife review:
1. Restore Linux Alt+Enter newline: textInput.tsx now uses
   k.shift || (isMac ? isActionMod(k) : k.meta) so Alt+Enter
   inserts a newline on Linux (was broken by isMac guard).
2. Fix image.attach response type: useComposerState.ts now uses
   ImageAttachResponse (which already has remainder) instead of
   InputDetectDropResponse with intersection.
3. Expand looksLikeDroppedPath test coverage with edge cases for
   image extensions, file:// URIs, spaces, empty input, and
   non-file URLs.
4. Make terminalParity.test.ts hermetic: terminalParityHints() now
   accepts optional fileOps/homeDir and passes them through to
   shouldPromptForTerminalSetup(), so tests inject mock readFile
   instead of hitting the real filesystem.

Fixes from Copilot inline review:
5. Remove unused options.now parameter from configureTerminalKeybindings.
6. Replace naive stripJsonComments (full-line // only) with a proper
   JSONC stripper that handles inline // comments, block comments,
   trailing commas, and preserves comment-like sequences in strings.
7. Move backupFile() call from immediately after read to right before
   write - backups are only created when changes will actually be
   written, not on every /terminal-setup invocation.

ui-tui/src/__tests__/terminalParity.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, vi } from 'vitest'
 
 import { terminalParityHints } from '../lib/terminalParity.js'
 
@@ -15,7 +15,30 @@ describe('terminalParityHints', () => {
   })
 
   it('suggests IDE setup only for VS Code-family terminals that still need bindings', async () => {
-    const hints = await terminalParityHints({ TERM_PROGRAM: 'vscode' } as NodeJS.ProcessEnv)
+    const readFile = vi.fn().mockRejectedValue(Object.assign(new Error('missing'), { code: 'ENOENT' }))
+
+    const hints = await terminalParityHints(
+      { TERM_PROGRAM: 'vscode' } as NodeJS.ProcessEnv,
+      { fileOps: { readFile }, homeDir: '/tmp/fake-home' }
+    )
     expect(hints.some(h => h.key === 'ide-setup')).toBe(true)
   })
+
+  it('suppresses IDE setup hint when keybindings are already configured', async () => {
+    const readFile = vi.fn().mockResolvedValue(
+      JSON.stringify([
+        { key: 'shift+enter', command: 'workbench.action.terminal.sendSequence', when: 'terminalFocus', args: { text: '\\\r\n' } },
+        { key: 'ctrl+enter', command: 'workbench.action.terminal.sendSequence', when: 'terminalFocus', args: { text: '\\\r\n' } },
+        { key: 'cmd+enter', command: 'workbench.action.terminal.sendSequence', when: 'terminalFocus', args: { text: '\\\r\n' } },
+        { key: 'cmd+z', command: 'workbench.action.terminal.sendSequence', when: 'terminalFocus', args: { text: '\u001b[122;9u' } },
+        { key: 'shift+cmd+z', command: 'workbench.action.terminal.sendSequence', when: 'terminalFocus', args: { text: '\u001b[122;10u' } }
+      ])
+    )
+
+    const hints = await terminalParityHints(
+      { TERM_PROGRAM: 'vscode' } as NodeJS.ProcessEnv,
+      { fileOps: { readFile }, homeDir: '/tmp/fake-home' }
+    )
+    expect(hints.some(h => h.key === 'ide-setup')).toBe(false)
+  })
 })

ui-tui/src/__tests__/terminalSetup.test.ts

@@ -30,6 +30,21 @@ describe('terminalSetup helpers', () => {
   it('strips line comments from keybindings JSON', () => {
     expect(stripJsonComments('// comment\n[{"key":"shift+enter"}]')).toBe('\n[{"key":"shift+enter"}]')
   })
+
+  it('strips inline comments and block comments', () => {
+    expect(stripJsonComments('[{"key":"a"} // inline\n]')).toBe('[{"key":"a"} \n]')
+    expect(stripJsonComments('[/* block */{"key":"a"}]')).toBe('[{"key":"a"}]')
+  })
+
+  it('removes trailing commas before ] or }', () => {
+    expect(JSON.parse(stripJsonComments('[{"key":"a"},]'))).toEqual([{ key: 'a' }])
+    expect(JSON.parse(stripJsonComments('[{"key":"a",}]'))).toEqual([{ key: 'a' }])
+  })
+
+  it('preserves comment-like sequences inside strings', () => {
+    const input = '[{"key":"a","args":{"text":"// not a comment"}}]'
+    expect(JSON.parse(stripJsonComments(input))).toEqual([{ key: 'a', args: { text: '// not a comment' } }])
+  })
 })
 
 describe('configureTerminalKeybindings', () => {
@@ -48,6 +63,7 @@ describe('configureTerminalKeybindings', () => {
     expect(result.success).toBe(true)
     expect(result.requiresRestart).toBe(true)
     expect(writeFile).toHaveBeenCalledTimes(1)
+    expect(copyFile).not.toHaveBeenCalled() // no existing file to back up
     const written = writeFile.mock.calls[0]?.[1] as string
     expect(written).toContain('shift+enter')
     expect(written).toContain('cmd+enter')
@@ -78,6 +94,24 @@ describe('configureTerminalKeybindings', () => {
     expect(result.success).toBe(false)
     expect(result.message).toContain('cmd+z')
     expect(writeFile).not.toHaveBeenCalled()
+    expect(copyFile).not.toHaveBeenCalled() // no backup when not writing
+  })
+
+  it('backs up existing keybindings.json only when writing changes', async () => {
+    const mkdir = vi.fn().mockResolvedValue(undefined)
+    const readFile = vi.fn().mockResolvedValue(JSON.stringify([]))
+    const writeFile = vi.fn().mockResolvedValue(undefined)
+    const copyFile = vi.fn().mockResolvedValue(undefined)
+
+    const result = await configureTerminalKeybindings('vscode', {
+      fileOps: { copyFile, mkdir, readFile, writeFile },
+      homeDir: '/Users/me',
+      platform: 'darwin'
+    })
+
+    expect(result.success).toBe(true)
+    expect(writeFile).toHaveBeenCalledTimes(1)
+    expect(copyFile).toHaveBeenCalledTimes(1) // backup created before writing
   })
 
   it('auto-detects the current IDE terminal', async () => {

ui-tui/src/__tests__/useComposerState.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, vi } from 'vitest'
 
 import { looksLikeDroppedPath } from '../app/useComposerState.js'
 
@@ -12,4 +12,38 @@ describe('looksLikeDroppedPath', () => {
     expect(looksLikeDroppedPath('hello world')).toBe(false)
     expect(looksLikeDroppedPath('line one\nline two')).toBe(false)
   })
+
+  it('recognizes common image file extensions', () => {
+    expect(looksLikeDroppedPath('/Users/me/Desktop/photo.jpg')).toBe(true)
+    expect(looksLikeDroppedPath('/Users/me/Desktop/diagram.png')).toBe(true)
+    expect(looksLikeDroppedPath('/tmp/capture.webp')).toBe(true)
+    expect(looksLikeDroppedPath('/tmp/image.gif')).toBe(true)
+  })
+
+  it('recognizes file:// URIs with various extensions', () => {
+    expect(looksLikeDroppedPath('file:///home/user/doc.pdf')).toBe(true)
+    expect(looksLikeDroppedPath('file:///tmp/screenshot.png')).toBe(true)
+  })
+
+  it('recognizes paths with spaces (not backslash-escaped)', () => {
+    expect(looksLikeDroppedPath('/var/folders/x/T/TemporaryItems/Screenshot 2026-04-21 at 1.04.43 PM.png')).toBe(true)
+  })
+
+  it('rejects empty/whitespace-only input', () => {
+    expect(looksLikeDroppedPath('')).toBe(false)
+    expect(looksLikeDroppedPath('   ')).toBe(false)
+    expect(looksLikeDroppedPath('\n')).toBe(false)
+  })
+
+  it('rejects URLs that are not file:// URIs', () => {
+    expect(looksLikeDroppedPath('https://example.com/image.png')).toBe(false)
+    expect(looksLikeDroppedPath('http://localhost/file.pdf')).toBe(false)
+  })
+
+  it('treats leading-slash strings as potential paths (server-side validates)', () => {
+    // The heuristic is intentionally broad — starts with / could be a path.
+    // Server-side image.attach / input.detect_drop does real validation.
+    expect(looksLikeDroppedPath('/help')).toBe(true)
+    expect(looksLikeDroppedPath('/model sonnet')).toBe(true)
+  })
 })