improve nix cache action & add binaries to cache

[insipx]

this adds the xdbg and xmtp_cli binaries to https://app.cachix.org/cache/xmtp#pins. building the binaries off main (with nix build .#xdbg) will download the already-built artifact rather than rebuild

adds a description to every crate

still need to verify they work (and fixes the broken fh cache on main that's been there for a while) but my nix flake update is broken b/c of github outage

[claude]

Claude finished @insipx's task —— View job

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Code Review Complete ✓

Review Checklist:

• Read and understand the CI workflow changes
• Review Nix flake configuration updates
• Review Cargo.toml changes across crates
• Check for potential issues not already covered
• Post final review feedback

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Review Feedback (2026-01-23, 21:56 UTC)

Critical Issue - CI Workflow

Runner mismatch in push-cachix job (.github/workflows/fh-cache.yml:41)

The build job uses warp-ubuntu-latest-x64-16x but the push-cachix job uses warp-ubuntu-latest-x86-16x (note: x64 vs x86). This means the artifact download will fail because the artifact names won't match.

# build job (line 15)
os: [warp-ubuntu-latest-x64-16x, macos-latest]

# push-cachix job (line 41)  
os: [warp-ubuntu-latest-x86-16x, macos-latest]  # ❌ Should be x64-16x

Fix: Change line 41 to use warp-ubuntu-latest-x64-16x to match the build job.

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Minor Observations

1. Nix configuration looks good: The rust-flake module integration is clean, and the auto-wiring setup with workspace globs is well-structured.

2. Cargo.toml descriptions: All crates now have descriptions added, which is excellent for documentation and crate publishing.

3. Fileset management: The nix/lib/filesets.nix uses proper Nix fileset unions and follows good practices for incremental builds.

4. CI job separation: The split into build → push-cachix → push-flakehub is a good pattern for reliability and only pushing to main.

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[macroscopeapp]

Build CI on warp-ubuntu-latest-x64-16x and macos-latest, cache with flakehub-cache-action using https://xmtp.cachix.org, and push binaries to Cachix and FlakeHub from fh-cache.yml

Updates CI to use FlakeHub caching with an upstream Cachix cache, adds a main-branch job that pushes build results to Cachix, and separates FlakeHub publishing into its own job; adjusts Nix flake to nixpkgs-unstable with rust-flake auto-wiring and updates workspace globs in Cargo.

📍Where to Start

Start with the workflow changes in fh-cache.yml, then review Nix flake outputs in flake.nix and Rust auto-wiring in nix/rust-defaults.nix.

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Macroscope summarized 875b45e.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.08%. Comparing base (236d4a4) to head (875b45e).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3020      +/-   ##
==========================================
+ Coverage   73.67%   74.08%   +0.41%     
==========================================
  Files         420      445      +25     
  Lines       54729    54372     -357     
==========================================
- Hits        40319    40279      -40     
+ Misses      14410    14093     -317     

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