build(linux-sandbox): always compile vendored bubblewrap on Linux; remove CODEX_BWRAP_ENABLE_FFI (#11498)

## Summary
This PR removes the temporary `CODEX_BWRAP_ENABLE_FFI` flag and makes
Linux builds always compile vendored bubblewrap support for
`codex-linux-sandbox`.

## Changes
- Removed `CODEX_BWRAP_ENABLE_FFI` gating from
`codex-rs/linux-sandbox/build.rs`.
- Linux builds now fail fast if vendored bubblewrap compilation fails
(instead of warning and continuing).
- Updated fallback/help text in
`codex-rs/linux-sandbox/src/vendored_bwrap.rs` to remove references to
`CODEX_BWRAP_ENABLE_FFI`.
- Removed `CODEX_BWRAP_ENABLE_FFI` env wiring from:
  - `.github/workflows/rust-ci.yml`
  - `.github/workflows/bazel.yml`
  - `.github/workflows/rust-release.yml`

---------

Co-authored-by: David Zbarsky <zbarsky@openai.com>

.github/workflows/rust-ci.yml

@@ -99,9 +99,6 @@ jobs:
       USE_SCCACHE: ${{ startsWith(matrix.runner, 'windows') && 'false' || 'true' }}
       CARGO_INCREMENTAL: "0"
       SCCACHE_CACHE_SIZE: 10G
-      # Keep cargo-based CI independent of system bwrap build deps.
-      # The bwrap FFI path is validated in Bazel workflows.
-      CODEX_BWRAP_ENABLE_FFI: "0"
 
     strategy:
       fail-fast: false
@@ -178,14 +175,18 @@ jobs:
 
     steps:
       - uses: actions/checkout@v6
-      - name: Install UBSan runtime (musl)
-        if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl' }}
+      - name: Install Linux build dependencies
+        if: ${{ runner.os == 'Linux' }}
         shell: bash
         run: |
           set -euo pipefail
           if command -v apt-get >/dev/null 2>&1; then
             sudo apt-get update -y
-            sudo DEBIAN_FRONTEND=noninteractive apt-get install -y libubsan1
+            packages=(pkg-config libcap-dev)
+            if [[ "${{ matrix.target }}" == 'x86_64-unknown-linux-musl' || "${{ matrix.target }}" == 'aarch64-unknown-linux-musl' ]]; then
+              packages+=(libubsan1)
+            fi
+            sudo DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends "${packages[@]}"
           fi
       - uses: dtolnay/rust-toolchain@1.93
         with:
@@ -447,9 +448,6 @@ jobs:
       USE_SCCACHE: ${{ startsWith(matrix.runner, 'windows') && 'false' || 'true' }}
       CARGO_INCREMENTAL: "0"
       SCCACHE_CACHE_SIZE: 10G
-      # Keep cargo-based CI independent of system bwrap build deps.
-      # The bwrap FFI path is validated in Bazel workflows.
-      CODEX_BWRAP_ENABLE_FFI: "0"
 
     strategy:
       fail-fast: false
@@ -485,6 +483,15 @@ jobs:
 
     steps:
       - uses: actions/checkout@v6
+      - name: Install Linux build dependencies
+        if: ${{ runner.os == 'Linux' }}
+        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 --no-install-recommends pkg-config libcap-dev
+          fi
       # Some integration tests rely on DotSlash being installed.
       # See https://github.com/openai/codex/pull/7617.
       - name: Install DotSlash