feat(build-time-versioning): apiserver -version flag and startup log

Declares GitCommit/BuildTime package vars (default "unknown", target of
task 4.1's -ldflags -X injection), a -version flag checked before
utils.PromptForTopDir()/InitLogger() (zero filesystem side effects), and
extends the existing "Initialize Logger done!" startup log line with
zap.String structured fields carrying both values, per design.md's
explicit mandate.

Live-verified end to end: -version output and the startup log's first
line are byte-identical, with a real commit id (matching
git rev-parse --short HEAD plus dirty suffix) and UTC timestamp -- the
first full round-trip proof in this spec (earlier Go tasks could only
verify via linked build-info metadata, since no consuming vars existed
yet).

Task 4.4/13 of build-time-versioning.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.kiro/specs/build-time-versioning/tasks.md

@@ -73,11 +73,10 @@
   - _Boundary: Makefile_
   - _Depends: 4.1_
 
-- [ ] 4.4 (P) apiserver: version flag, vars, and startup log
-  - Declare `GitCommit`/`BuildTime` package vars (default `unknown`) in `src/frontend/apiserver/cmd/main.go`
-  - Add a `-version` flag, checked before `utils.InitLogger()`, that prints both values and exits with no logging side effects
-  - Extend the existing `logger.Info("********** Initialize Logger done!")` call site to also log both values
-  - Observable: `xce_apiserver -version` prints both values and exits without starting the server; the startup log's first lines include the identical two values
+- [x] 4.4 (P) apiserver: version flag, vars, and startup log
+  - `GitCommit`/`BuildTime` package vars (default `unknown`); `-version` flag checked before `utils.PromptForTopDir`/`utils.InitLogger()`, zero filesystem side effects (live-verified: no logs dir created)
+  - Startup log extended via `zap.String("gitCommit", ...)`/`zap.String("buildTime", ...)` structured fields on the existing `"Initialize Logger done!"` line, per design.md's explicit mandate
+  - Observable confirmed live (independently re-verified by review, full round trip): `-version` and the startup log's first line are byte-identical (`45c9b026-dirty`, matching `git rev-parse --short HEAD` + dirty suffix, and a real UTC timestamp)
   - _Requirements: 1.1, 1.2, 2.1, 2.2, 3.1, 3.2_
   - _Boundary: apiserver/cmd/main.go_
   - _Depends: 4.1_

src/frontend/apiserver/cmd/main.go

@@ -21,12 +21,26 @@ import (
 	"go.uber.org/zap"
 )
 
+// GitCommit and BuildTime are injected at link time via
+// `-ldflags "-X main.GitCommit=... -X main.BuildTime=..."` (see
+// src/tools/go_build and src/frontend/Makefile's build-server target). The
+// "unknown" defaults matter: a bare `go build`/`go run` that bypasses that
+// ldflags injection must still report "unknown" rather than an empty
+// string, matching this feature's unknown-fallback requirement (see
+// xce_version_field() in src/lib/utils.c for the equivalent C-side
+// convention).
+var (
+	GitCommit = "unknown"
+	BuildTime = "unknown"
+)
+
 func main() {
 	gin.SetMode(gin.ReleaseMode)
 	gin.DefaultWriter = io.Discard
 	gin.DefaultErrorWriter = io.Discard
 
 	topDir := flag.String("d", "", "Top directory (default: current directory)")
+	versionFlag := flag.Bool("version", false, "Print version information and exit")
 	flag.Usage = func() {
 		fmt.Fprintln(os.Stderr, `
 	Usage: apiserver -d <top_directory>
@@ -35,12 +49,22 @@ func main() {
 	}
 	flag.Parse()
 
+	// Checked before utils.InitLogger() runs so -version has no logging
+	// side effects: it must only print and exit, matching controller's/
+	// scheduler's/worker's own --version contract (Requirement 2.1).
+	if *versionFlag {
+		fmt.Printf("xce-apiserver %s built %s\n", GitCommit, BuildTime)
+		return
+	}
+
 	utils.Global_TopDir = utils.PromptForTopDir(topDir)
 
 	if err := utils.InitLogger(); err != nil {
 		os.Exit(1)
 	}
-	logger.Info("********** Initialize Logger done!")
+	logger.Info("********** Initialize Logger done!",
+		zap.String("gitCommit", GitCommit),
+		zap.String("buildTime", BuildTime))
 
 	if err := utils.InitConf(); err != nil {
 		logger.Error("Failed to initialize configuration files", zap.Error(err))