doc.go: Package documentation explaining convention-based extensibility pattern. Each file = one annotation concept, each with GetXxx() functions.

http_config.go:

• HTTPConfig struct: Path string, Method string, PathParams []string (same as existing but exported)
• ServiceConfig struct: BasePath string (replaces both ServiceConfigImpl and ServiceHTTPConfig names)
• GetMethodHTTPConfig(method *protogen.Method) *HTTPConfig -- extracts HTTP config from method options. Uses HTTPMethodToString() for the Method field (uppercase). Identical logic to existing getMethodHTTPConfig across all 4 generators.
• GetServiceBasePath(service *protogen.Service) string -- extracts base path from service options. Returns empty string if not configured. Simpler API than returning a struct with one field.

headers.go:

• GetServiceHeaders(service *protogen.Service) []*http.Header -- identical to existing
• GetMethodHeaders(method *protogen.Method) []*http.Header -- identical to existing
• CombineHeaders(serviceHeaders, methodHeaders []*http.Header) []*http.Header -- merges with method precedence, sorted by name. Extracted from openapiv3. Use sort.Strings instead of bubble sort.

query.go:

• QueryParam struct: ALL fields from all generators combined:
  • FieldName string (proto field name)
  • FieldGoName string (Go field name)
  • FieldJSONName string (JSON field name / camelCase)
  • ParamName string (query parameter name)
  • Required bool
  • FieldKind string (proto field kind: string, int32, bool, etc.)
  • Field *protogen.Field (raw protogen field reference)
• GetQueryParams(message *protogen.Message) []QueryParam -- populates ALL fields for each param. Use field.GoName for FieldGoName, field.Desc.JSONName() for FieldJSONName, field.Desc.Kind().String() for FieldKind, and pass field directly for the Field reference.

unwrap.go:

• UnwrapFieldInfo struct: same as httpgen's (Field, ElementType, IsRootUnwrap, IsMapField)
• UnwrapValidationError struct: same as httpgen's (MessageName, FieldName, Reason) with Error() method
• HasUnwrapAnnotation(field *protogen.Field) bool -- identical to existing
• GetUnwrapField(message *protogen.Message) (*UnwrapFieldInfo, error) -- full validation version from httpgen (validates non-repeated/non-map, multiple unwrap fields, map-without-root-unwrap). Return nil, nil for no unwrap field (with nolint comment).
• FindUnwrapField(message *protogen.Message) *protogen.Field -- simple version from tsclientgen/openapiv3: returns the unwrap-annotated repeated field or nil. No validation, no error.
• IsRootUnwrap(message *protogen.Message) bool -- from tsclientgen: single field with unwrap=true

field_examples.go:

• GetFieldExamples(field *protogen.Field) []string -- identical to existing

path.go:

• Unexported pathParamRegex (package-level compiled regex, same as existing)
• ExtractPathParams(path string) []string -- identical to existing
• BuildHTTPPath(servicePath, methodPath string) string -- from openapiv3's buildHTTPPath
• EnsureLeadingSlash(path string) string -- from openapiv3's ensureLeadingSlash (export it since generators may need it)

method.go:

• HTTPMethodToString(m http.HttpMethod) string -- returns UPPERCASE ("GET", "POST", etc.). Default POST for unspecified.
• HTTPMethodToLower(m http.HttpMethod) string -- returns lowercase ("get", "post", etc.) for OpenAPI. Uses strings.ToLower(HTTPMethodToString(m)) for DRY.

helpers.go:

• LowerFirst(s string) string -- converts "FooBar" to "fooBar". Identical to existing 3 copies.

IMPORTANT: Do NOT import any generator package (httpgen, clientgen, tsclientgen, openapiv3). Only import: stdlib, protogen, proto, descriptorpb, sebuf/http.

After creating files, run go build ./internal/annotations/ to verify compilation, then run make lint-fix to catch any linting issues. go build ./internal/annotations/ succeeds with zero errors. make lint-fix produces no errors. go vet ./internal/annotations/ produces no warnings. All 9 files exist in internal/annotations/, package compiles, no import cycles.