Title: view refuses files whose path is longer than 256 characters in non-interactive runs ("Permission denied and could not request permission from user") #5095

Describe the bug

Environment

• Copilot CLI 1.0.86-0, 1.0.89-3 and 1.0.89 on Windows 11. Windows long paths
  are enabled (LongPathsEnabled = 1).
• Non-interactive child process, roughly:
  copilot -C --no-ask-user --no-custom-instructions --disable-builtin-mcps
  --available-tools=view,rg,glob --deny-tool=write --deny-tool=shell
  --output-format=json (prompt supplied non-interactively)

Steps to reproduce

1. Create a directory D. Inside it, create file F whose full path is 257 or more
   characters, and file G whose full path is 256 characters or fewer.
2. Run the CLI non-interactively with -C D --no-ask-user and ask it to view F and G.

Actual

• view of G succeeds.
• view of F fails with: "Permission denied and could not request permission from user".
• rg over D still returns matching lines from F, so the file itself is readable.

Expected

• F is inside the allowed working directory, so view should succeed.
• If there is a path-length limit, the error should say so, rather than report
  a permission problem.

Evidence (production runs, 2026-09-23 to 2026-10-06)

• 227 view calls across 7 sessions. All 218 successful reads had paths of 256
  characters or fewer. All 7 denied reads of real files inside the -C directory
  had paths of 257-264 characters.
• The same files were denied consistently across sessions.
• Windows long paths are enabled, so the operating system is not the cause.

Impact

• In unattended runs the agent cannot ask for permission, so it silently
  continues without the file. The error message points to permissions, not
  path length, which makes the cause hard to find.

Note

• These observations come from real unattended runs; I have not yet run a
  controlled minimal repro. Not checked: whether an interactive session
  prompts instead of denying, and whether glob is affected.

Affected version

No response

Steps to reproduce the behavior

No response

Expected behavior

No response

Additional context

No response