bash tool fails inside devenv shell with bash 5.3 — "Invalid shell ID: 0 / no active shell sessions"

### Describe the bug

The Copilot CLI bash tool silently fails when the shell session is using bash 5.3.x. Every bash call appears to succeed but no shellId is returned, and subsequent read_bash calls fail with:

Invalid shell ID: 0. Please supply a valid shell ID to read output from.

### Affected version

1.0.32 run within newest devenv from nixos-unstable

### Steps to reproduce the behavior

1. Install devenv (https://devenv.sh)
2.x (it pins bashInteractive from nixpkgs-unstable, currently 5.3.9)
2. Enter devenv shell
3. Launch copilot from within the devenv shell
4. Ask the agent to run any bash command (e.g. echo hello)
5. Agent reports no active shell sessions — bash tool is completely non-functional

### Expected behavior

_No response_

### Additional context

Works fine outside devenv (system bash 5.2.37). Also works in other AI coding tools (e.g. OpenCode) that don't rely on a persistent PTY session.

### Workaround

Shim bash in PATH to point to bash 5.2:
mkdir -p /tmp/bash-shim
ln -sfn /usr/bin/bash-5.2 /tmp/bash-shim/bash # adjust path for your system
export PATH="/tmp/bash-shim:$PATH"

Then launch copilot — bash tool works.
In short: looks like copilot have problem with newest bash Version: 5.3p9 from nixos-unstable.

Reproduce the bash tool inside a devenv shell using bash 5.3.9, then compare it with bash 5.2.37 and the documented PATH shim; start by tracing the persistent PTY shell session and shellId handling. Done means bash calls return a valid shellId and read_bash retrieves output in the affected environment.

索引モデルが issue の本文から書いたものです。