🤖 Optimize make static-check (74% faster) (#288)

Speeds up static-check from **18.5s to 4.8s** for incremental changes
(74% improvement).

## Changes

1. **Enable parallel-by-default** - Add `MAKEFLAGS += -j` to Makefile
   - Independent checks (lint, typecheck, fmt-check) run concurrently
   - Cold cache: 18.5s → 13s

2. **Enable ESLint caching** - Add `--cache` flag to scripts/lint.sh  
   - Caches lint results per file, only re-lints changed files
   - Incremental: 13s → ~1s (only changed files re-linted)

## Performance

| Scenario | Before | After | Improvement |
|----------|--------|-------|-------------|
| Cold cache (CI) | 18.5s | 13s | 30% faster |
| Hot cache (dev) | 18.5s | 4.8s | **74% faster** |

## Implementation Details

### Parallel-by-default
- Added `MAKEFLAGS += -j` to enable parallel execution by default
- Updated documentation to reflect new behavior (use `-j1` for
sequential)
- Existing `.NOTPARALLEL` directive for build-main ensures safety where
needed

### ESLint cache
- Cache file (`.eslintcache`) stores lint results keyed by file content
- Automatically invalidates on ESLint config changes
- Gitignored to avoid committing cache state

## Testing

Verified performance with:
- Clean cache (simulates CI): Full lint takes 13s
- Hot cache + small change: Lint takes ~1s (only changed files)
- Full static-check with hot cache: 4.8s total

_Generated with `cmux`_

Author: ammar-agent

.gitignore

@@ -53,6 +53,9 @@ yarn-error.log
 # testing
 /coverage
 
+# ESLint cache for faster incremental lints
+.eslintcache
+
 # Bun
 bun.lockb
 dist

Makefile

@@ -10,7 +10,8 @@
 #   make test          - Run tests
 #
 # Parallelism:
-#   Use make -jN to run independent tasks concurrently (e.g., make -j4 build)
+#   Runs in parallel by default for faster builds. Use -j1 for sequential execution.
+#   Individual targets can opt out with .NOTPARALLEL if needed.
 #
 # Backwards Compatibility:
 #   All commands also work via `bun run` (e.g., `bun run dev` calls `make dev`)
@@ -23,6 +24,11 @@
 #   Branches reduce reproducibility - builds should fail fast with clear errors
 #   if dependencies are missing, not silently fall back to different behavior.
 
+# Enable parallel execution by default (only if user didn't specify -j)
+ifeq (,$(filter -j%,$(MAKEFLAGS)))
+MAKEFLAGS += -j
+endif
+
 # Include formatting rules
 include fmt.mk
 

scripts/lint.sh

@@ -26,9 +26,9 @@ ESLINT_PATTERN='src/**/*.{ts,tsx}'
 
 if [ "$1" = "--fix" ]; then
   echo "Running bun x eslint with --fix..."
-  bun x eslint "$ESLINT_PATTERN" --fix
+  bun x eslint --cache "$ESLINT_PATTERN" --fix
 else
   echo "Running eslint..."
-  bun x eslint "$ESLINT_PATTERN"
+  bun x eslint --cache "$ESLINT_PATTERN"
   echo "ESLint checks passed!"
 fi