♻️ Decouple bun and uv from binary, resolve at runtime with auto-download

[renardeinside]

Summary

• Remove bun embedding from the binary (include_bytes!), reducing size from ~99MB to ~39MB
• Add runtime resolution for both bun (v1.3.8) and uv (v0.10.3) with 4-tier fallback: env var override → system PATH → ~/.apx/bin/ cache → auto-download from GitHub releases
• Simplify CI by removing bun binary download/cache steps from release workflow

Details

New module: crates/core/src/download.rs

Central binary resolution and auto-download logic. Uses tokio::sync::OnceCell for per-process caching. Provides both async (resolve_bun/uv) and sync (try_resolve_bun/uv) APIs.

Key changes

• BunCommand::new(), UvCommand::new(), ApxCommand::new() are now async and return Result
• All ~20 call sites updated to .await?
• Removed ensure_bun_extracted(), bun_binary_path(), copy_bun_binary() build step
• Deleted scripts/get_binaries.py (no longer needed)
• Install scripts updated to inform users that uv will be auto-downloaded

User experience

• Download progress printed to stderr (bun not found on PATH — downloading v1.3.8...)
• Actionable error messages on failure (Failed to auto-install bun v1.3.8: ... Install bun manually or set APX_BUN_PATH)
• No stdout noise (MCP-safe)

Test plan

• cargo clippy --workspace -- -D warnings passes clean
• cargo test -p apx-core -p apx-cli — 120 tests pass
• Binary size ~39MB (down from ~99MB)
• With system bun/uv on PATH: uses system binaries
• Without bun on PATH: auto-downloads bun v1.3.8 to ~/.apx/bin/
• Without uv on PATH: auto-downloads uv v0.10.3 to ~/.apx/bin/
• Version markers written (~/.apx/bin/.bun-version, .uv-version)

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