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Fix macOS build bundling wrong macmon binary (#1797)

f318f9ea14a3323259ff98528f62624c37f9a5a5 · 2026-03-26 02:47:48 -0700 · Alex Cheema

## Motivation

PR #1747 fixed macmon support for M5 Pro/Max by pinning the
`swiftraccoon/macmon` fork in `flake.nix`. This works when running from
source (via Nix) but the distributed macOS `.app` build was still broken
on M5 Pro/Max because it was bundling the wrong macmon.

The error on M5 Pro/Max:
```
macmon preflight failed with return code -6: thread 'main' panicked at src/sources.rs:394:41
```

## Changes

- Removed `macmon` from `brew install` in `build-app.yml` — this was
installing the upstream `vladkens/macmon` which doesn't support M5
Pro/Max
- Added a new step that resolves the pinned macmon fork from the Nix dev
shell (same `swiftraccoon/macmon` at rev `9154d23` already defined in
`flake.nix`) and adds it to `$GITHUB_PATH`
- Added a safety `brew uninstall macmon` to ensure no Homebrew macmon
can shadow the pinned version

## Why It Works

PyInstaller bundles macmon via `shutil.which("macmon")`. Previously this
found the Homebrew (upstream) binary. Now it finds the Nix-overlayed
fork that has M5 Pro/Max support, because `$GITHUB_PATH` prepends the
Nix store path before the PyInstaller step runs.

## Test Plan

### Manual Testing
<!-- Hardware: M5 Pro -->
- Trigger a macOS build and verify the bundled macmon is the pinned fork
- Run the built `.app` on M5 Pro/Max and confirm macmon preflight
succeeds

### Automated Testing
- Existing CI build workflow will validate that the macmon binary is
found and bundled correctly

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Files touched

Diff

commit f318f9ea14a3323259ff98528f62624c37f9a5a5
Author: Alex Cheema <41707476+AlexCheema@users.noreply.github.com>
Date:   Thu Mar 26 02:47:48 2026 -0700

    Fix macOS build bundling wrong macmon binary (#1797)
    
    ## Motivation
    
    PR #1747 fixed macmon support for M5 Pro/Max by pinning the
    `swiftraccoon/macmon` fork in `flake.nix`. This works when running from
    source (via Nix) but the distributed macOS `.app` build was still broken
    on M5 Pro/Max because it was bundling the wrong macmon.
    
    The error on M5 Pro/Max:
    ```
    macmon preflight failed with return code -6: thread 'main' panicked at src/sources.rs:394:41
    ```
    
    ## Changes
    
    - Removed `macmon` from `brew install` in `build-app.yml` — this was
    installing the upstream `vladkens/macmon` which doesn't support M5
    Pro/Max
    - Added a new step that resolves the pinned macmon fork from the Nix dev
    shell (same `swiftraccoon/macmon` at rev `9154d23` already defined in
    `flake.nix`) and adds it to `$GITHUB_PATH`
    - Added a safety `brew uninstall macmon` to ensure no Homebrew macmon
    can shadow the pinned version
    
    ## Why It Works
    
    PyInstaller bundles macmon via `shutil.which("macmon")`. Previously this
    found the Homebrew (upstream) binary. Now it finds the Nix-overlayed
    fork that has M5 Pro/Max support, because `$GITHUB_PATH` prepends the
    Nix store path before the PyInstaller step runs.
    
    ## Test Plan
    
    ### Manual Testing
    <!-- Hardware: M5 Pro -->
    - Trigger a macOS build and verify the bundled macmon is the pinned fork
    - Run the built `.app` on M5 Pro/Max and confirm macmon preflight
    succeeds
    
    ### Automated Testing
    - Existing CI build workflow will validate that the macmon binary is
    found and bundled correctly
    
    Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 .github/workflows/build-app.yml | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/.github/workflows/build-app.yml b/.github/workflows/build-app.yml
index d20bfc12..c0cb0e9b 100644
--- a/.github/workflows/build-app.yml
+++ b/.github/workflows/build-app.yml
@@ -159,7 +159,7 @@ jobs:
           fi
 
       - name: Install Homebrew packages
-        run: brew install just awscli macmon
+        run: brew install just awscli
 
       - name: Install UV
         uses: astral-sh/setup-uv@v6
@@ -243,6 +243,14 @@ jobs:
       # Build the bundle
       # ============================================================
 
+      - name: Add pinned macmon to PATH
+        run: |
+          MACMON_DIR=$(nix develop --command sh -c 'dirname $(which macmon)')
+          echo "Using macmon from: $MACMON_DIR"
+          echo "$MACMON_DIR" >> $GITHUB_PATH
+          # Remove any Homebrew macmon so PyInstaller can't accidentally pick it up
+          brew uninstall macmon 2>/dev/null || true
+
       - name: Build PyInstaller bundle
         run: uv run pyinstaller packaging/pyinstaller/exo.spec

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