refactor: delete exec-server and move execve wrapper into shell-escalation (#12632)

## Why

We already plan to remove the shell-tool MCP path, and doing that
cleanup first makes the follow-on `shell-escalation` work much simpler.

This change removes the last remaining reason to keep
`codex-rs/exec-server` around by moving the `codex-execve-wrapper`
binary and shared shell test fixtures to the crates/tests that now own
that functionality.

## What Changed

### Delete `codex-rs/exec-server`

- Remove the `exec-server` crate, including the MCP server binary,
MCP-specific modules, and its test support/test suite
- Remove `exec-server` from the `codex-rs` workspace and update
`Cargo.lock`

### Move `codex-execve-wrapper` into `codex-rs/shell-escalation`

- Move the wrapper implementation into `shell-escalation`
(`src/unix/execve_wrapper.rs`)
- Add the `codex-execve-wrapper` binary entrypoint under
`shell-escalation/src/bin/`
- Update `shell-escalation` exports/module layout so the wrapper
entrypoint is hosted there
- Move the wrapper README content from `exec-server` to
`shell-escalation/README.md`

### Move shared shell test fixtures to `app-server`

- Move the DotSlash `bash`/`zsh` test fixtures from
`exec-server/tests/suite/` to `app-server/tests/suite/`
- Update `app-server` zsh-fork tests to reference the new fixture paths

### Keep `shell-tool-mcp` as a shell-assets package

- Update `.github/workflows/shell-tool-mcp.yml` packaging so the npm
artifact contains only patched Bash/Zsh payloads (no Rust binaries)
- Update `shell-tool-mcp/package.json`, `shell-tool-mcp/src/index.ts`,
and docs to reflect the shell-assets-only package shape
- `shell-tool-mcp-ci.yml` does not need changes because it is already
JS-only

## Verification

- `cargo shear`
- `cargo clippy -p codex-shell-escalation --tests`
- `just clippy`

.github/workflows/shell-tool-mcp.yml

@@ -67,128 +67,6 @@ jobs:
           echo "npm_tag=${npm_tag}" >> "$GITHUB_OUTPUT"
           echo "should_publish=${should_publish}" >> "$GITHUB_OUTPUT"
 
-  rust-binaries:
-    name: Build Rust - ${{ matrix.target }}
-    needs: metadata
-    runs-on: ${{ matrix.runner }}
-    timeout-minutes: 30
-    env:
-      CARGO_PROFILE_RELEASE_LTO: ${{ contains(needs.metadata.outputs.version, '-alpha') && 'thin' || 'fat' }}
-    defaults:
-      run:
-        working-directory: codex-rs
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - runner: macos-15-xlarge
-            target: aarch64-apple-darwin
-          - runner: macos-15-xlarge
-            target: x86_64-apple-darwin
-          - runner: ubuntu-24.04
-            target: x86_64-unknown-linux-musl
-            install_musl: true
-          - runner: ubuntu-24.04-arm
-            target: aarch64-unknown-linux-musl
-            install_musl: true
-    steps:
-      - name: Checkout repository
-        uses: actions/checkout@v6
-
-      - name: Install UBSan runtime (musl)
-        if: ${{ matrix.install_musl }}
-        shell: bash
-        run: |
-          set -euo pipefail
-          if command -v apt-get >/dev/null 2>&1; then
-            sudo apt-get update -y
-            sudo DEBIAN_FRONTEND=noninteractive apt-get install -y libubsan1
-          fi
-
-      - uses: dtolnay/rust-toolchain@1.93.0
-        with:
-          targets: ${{ matrix.target }}
-
-      - if: ${{ matrix.install_musl }}
-        name: Install Zig
-        uses: mlugg/setup-zig@v2
-        with:
-          version: 0.14.0
-
-      - if: ${{ matrix.install_musl }}
-        name: Install musl build dependencies
-        env:
-          TARGET: ${{ matrix.target }}
-        run: bash "${GITHUB_WORKSPACE}/.github/scripts/install-musl-build-tools.sh"
-
-      - if: ${{ matrix.install_musl }}
-        name: Configure rustc UBSan wrapper (musl host)
-        shell: bash
-        run: |
-          set -euo pipefail
-          ubsan=""
-          if command -v ldconfig >/dev/null 2>&1; then
-            ubsan="$(ldconfig -p | grep -m1 'libubsan\.so\.1' | sed -E 's/.*=> (.*)$/\1/')"
-          fi
-          wrapper_root="${RUNNER_TEMP:-/tmp}"
-          wrapper="${wrapper_root}/rustc-ubsan-wrapper"
-          cat > "${wrapper}" <<EOF
-          #!/usr/bin/env bash
-          set -euo pipefail
-          if [[ -n "${ubsan}" ]]; then
-            export LD_PRELOAD="${ubsan}\${LD_PRELOAD:+:\${LD_PRELOAD}}"
-          fi
-          exec "\$1" "\${@:2}"
-          EOF
-          chmod +x "${wrapper}"
-          echo "RUSTC_WRAPPER=${wrapper}" >> "$GITHUB_ENV"
-          echo "RUSTC_WORKSPACE_WRAPPER=" >> "$GITHUB_ENV"
-
-      - if: ${{ matrix.install_musl }}
-        name: Clear sanitizer flags (musl)
-        shell: bash
-        run: |
-          set -euo pipefail
-          # Clear global Rust flags so host/proc-macro builds don't pull in UBSan.
-          echo "RUSTFLAGS=" >> "$GITHUB_ENV"
-          echo "CARGO_ENCODED_RUSTFLAGS=" >> "$GITHUB_ENV"
-          echo "RUSTDOCFLAGS=" >> "$GITHUB_ENV"
-          # Override any runner-level Cargo config rustflags as well.
-          echo "CARGO_BUILD_RUSTFLAGS=" >> "$GITHUB_ENV"
-          echo "CARGO_TARGET_X86_64_UNKNOWN_LINUX_GNU_RUSTFLAGS=" >> "$GITHUB_ENV"
-          echo "CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_RUSTFLAGS=" >> "$GITHUB_ENV"
-          echo "CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_RUSTFLAGS=" >> "$GITHUB_ENV"
-          echo "CARGO_TARGET_AARCH64_UNKNOWN_LINUX_MUSL_RUSTFLAGS=" >> "$GITHUB_ENV"
-
-          sanitize_flags() {
-            local input="$1"
-            input="${input//-fsanitize=undefined/}"
-            input="${input//-fno-sanitize-recover=undefined/}"
-            input="${input//-fno-sanitize-trap=undefined/}"
-            echo "$input"
-          }
-
-          cflags="$(sanitize_flags "${CFLAGS-}")"
-          cxxflags="$(sanitize_flags "${CXXFLAGS-}")"
-          echo "CFLAGS=${cflags}" >> "$GITHUB_ENV"
-          echo "CXXFLAGS=${cxxflags}" >> "$GITHUB_ENV"
-
-      - name: Build exec server binaries
-        run: cargo build --release --target ${{ matrix.target }} --bin codex-exec-mcp-server --bin codex-execve-wrapper
-
-      - name: Stage exec server binaries
-        run: |
-          dest="${GITHUB_WORKSPACE}/artifacts/vendor/${{ matrix.target }}"
-          mkdir -p "$dest"
-          cp "target/${{ matrix.target }}/release/codex-exec-mcp-server" "$dest/"
-          cp "target/${{ matrix.target }}/release/codex-execve-wrapper" "$dest/"
-
-      - uses: actions/upload-artifact@v6
-        with:
-          name: shell-tool-mcp-rust-${{ matrix.target }}
-          path: artifacts/**
-          if-no-files-found: error
-
   bash-linux:
     name: Build Bash (Linux) - ${{ matrix.variant }} - ${{ matrix.target }}
     needs: metadata
@@ -537,7 +415,6 @@ jobs:
     name: Package npm module
     needs:
       - metadata
-      - rust-binaries
       - bash-linux
       - bash-darwin
       - zsh-linux
@@ -579,7 +456,6 @@ jobs:
           mkdir -p "$staging" "$staging/vendor"
           cp shell-tool-mcp/README.md "$staging/"
           cp shell-tool-mcp/package.json "$staging/"
-          cp -R shell-tool-mcp/bin "$staging/"
 
           found_vendor="false"
           shopt -s nullglob
@@ -613,8 +489,6 @@ jobs:
           set -euo pipefail
           staging="${{ steps.staging.outputs.dir }}"
           chmod +x \
-            "$staging"/vendor/*/codex-exec-mcp-server \
-            "$staging"/vendor/*/codex-execve-wrapper \
             "$staging"/vendor/*/bash/*/bash \
             "$staging"/vendor/*/zsh/*/zsh