feat: add Android/Termux support and stable file locking

[pchuri]

This PR fixes Android/Termux builds and replaces nightly file locking with a stable approach.

Why

• Android/Termux lacks platform support for arboard, causing build failures in the TUI crate.
• The core crate used nightly-only file locking APIs; now uses stable std::fs file locking (Rust 1.89+).

Changes

• tui: gate arboard under cfg(all(unix, not(target_os = "android"))).
• tui: add Android stubs in clipboard_paste.rs returning a clear ClipboardUnavailable error.
• core: use stabilized std::fs::File::try_lock() in message_history.rs for advisory file locks.
• tests: updated a single TUI snapshot due to improved wrapping of long diff lines.
• fix: restore missing tempfile::Builder import that was accidentally removed
• refactor: modernize format! macros with string interpolation throughout codebase

Technical Details

Android Support

• Problem: arboard crate doesn't support Android/Termux, causing compilation failures
• Solution: Conditional compilation with cfg(all(unix, not(target_os = "android")))
• Fallback: Clear error messages for Android users attempting clipboard operations

File Locking Migration

• From: Nightly-only file locking APIs
• To: Stabilized std::fs::File::try_lock() and try_lock_shared() (Rust 1.89+)
• Benefits: No external dependencies, cross-platform compatibility, stable API
• Compatibility: Maintains same advisory locking semantics with retry logic

Impact

• Android/Termux builds succeed.
• Clipboard image paste is disabled on Android with a clear message; all other platforms unaffected.
• Stable file locking across platforms using standard library (no external dependencies).

Validation

• Ran just fmt and just fix -p codex-core / -p codex-tui.
• cargo test -p codex-tui: all pass after snapshot update.
• cargo check --target aarch64-linux-android -p codex-tui: arboard dependency correctly gated
• Local builds on macOS succeed with all tests passing
• Full suite has environment-specific failures in exec tests on Termux (e.g., missing /bin/bash) not related to these changes.

[bolinfest]

The core crate used nightly-only file locking APIs; replace with stable fd-lock for cross-platform advisory locks.

I thought this was stable in 1.89?

https://blog.rust-lang.org/2025/08/07/Rust-1.89.0/#stabilized-apis

[pchuri]

You're absolutely right! Thank you for pointing that out.

I initially used fd-lock as an external dependency, but you're correct that std::fs::File::lock was stabilized in Rust 1.89.

I've just updated the implementation in commit 6a29eb8 to use the stabilized standard library APIs (try_lock() and try_lock_shared()) instead of the external fd-lock crate.

[bolinfest]

@pchuri I just enabled uninlined_format_args for the workspace in #2845, so please rebase your PR on top of it so your PR doesn't have unrelated changes.

Relatedly, could you please split this into two PRs: one for the file lock stuff and one for gating the arboard dependency? These are separate concerns and I expect we can get things resolved quicker this way.

[pchuri]

@bolinfest Done! I've split this into two separate PRs as requested:

1. File Locking PR feat: add stable file locking using std::fs APIs #2894:

   • Uses Rust 1.89+ stabilized std::fs::File locking APIs
   • Cross-platform implementation with Windows/Unix compatibility
   • No external dependencies

2. Android/Termux Support PR feat: add Android/Termux support by gating arboard dependency #2895:

   • Gates arboard dependency for Android targets
   • Fixes compilation issues on Android/Termux
   • Maintains clipboard functionality on other platforms

Both PRs are rebased on the latest main branch that includes the uninlined_format_args changes from #2845. This should make the review process much cleaner and faster.

Thank you for the guidance on splitting these concerns

[pchuri]

Closing this PR in favor of two separate PRs that address distinct concerns:

• File locking: feat: add stable file locking using std::fs APIs #2894
• Android/Termux support: feat: add Android/Termux support by gating arboard dependency #2895

This provides cleaner separation of concerns and easier review process as requested by @bolinfest.