Refactor: align codebase with engineering standards

.github/workflows/ci.yml

@@ -14,16 +14,13 @@ jobs:
 
       - uses: actions/setup-go@v5
         with:
-          go-version: '1.21'
+          go-version: '1.24'
 
-      - name: Download dependencies
-        run: go mod download
+      - name: Tidy, test, and build
+        run: make tidy test build
 
-      - name: Build
-        run: go build -v ./...
-
-      - name: Test
-        run: go test -v -race -coverprofile=coverage.out ./...
+      - name: Coverage gate
+        run: make test-cover-check
 
   lint:
     runs-on: ubuntu-latest
@@ -32,7 +29,7 @@ jobs:
 
       - uses: actions/setup-go@v5
         with:
-          go-version: '1.21'
+          go-version: '1.24'
 
       - name: golangci-lint
         uses: golangci/golangci-lint-action@v7

.golangci.yml

@@ -3,11 +3,15 @@ version: "2"
 linters:
   enable:
     - errcheck
+    - errorlint
+    - exhaustive
     - govet
+    - gosec
     - ineffassign
+    - misspell
+    - revive
     - staticcheck
     - unused
-    - misspell
   settings:
     errcheck:
       exclude-functions:
@@ -19,9 +23,18 @@ linters:
       - path: _test\.go
         linters:
           - errcheck
+          - gosec
       - linters:
           - errcheck
         source: "defer.*\\.Close\\(\\)"
+      # Stuttering names (e.g., mail.MailClient) are accepted for clarity at call sites
+      - linters:
+          - revive
+        text: "stutters"
+      # Standard library package name conflicts are intentional (e.g., calendar, contacts)
+      - linters:
+          - revive
+        text: "avoid package names that conflict"
 
 formatters:
   enable: