G0 D1 hardened: 3-lineage scrum review on shipped code · 7 fixes applied

Code-review pass after D1 shipped, all three model lineages running
in parallel against the actual Go source (not docs):

Convergent findings (≥2 reviewers — high confidence):
- C1 BLOCK · Run() errCh/select race could silently drop fast bind
  errors. Fixed: net.Listen() now runs synchronously before the
  goroutine; bind errors surface as Run()'s return value.
- C2 BLOCK · scripts/d1_smoke.sh sleep 0.5 races bind on cold boxes.
  Fixed: replaced with poll_health() loop, 5s/svc budget, 50ms poll.
- C3 WARN · LoadConfig silent fallback when file missing. Fixed:
  emits slog.Warn with path + hint when path given but file absent.

Single-reviewer fixes:
- S1 WARN · slog.SetDefault inside Run() mutated global state from a
  library function. Fixed: Run() no longer calls SetDefault.
- S2 WARN · os.IsNotExist → errors.Is(err, fs.ErrNotExist) idiom.
- S6 WARN · smoke double-curl collapsed to single curl -i parse.

Second-pass Opus review on post-fix code caught one more:
- head -1 on curl -i fragile against 1xx interim lines. Fixed:
  awk picks the last HTTP/* status line (robust to 100 Continue).

Accepted with rationale (deferred or planned):
- S3 secrets-in-lakehouse.toml: D2.3 SecretsProvider already planned
- S4 5x cmd/*/main.go duplication: defer until D2 reveals real
  per-service config consumption
- S5 /health log volume: defer post-G0, not on k8s yet
- 2nd-pass theoreticals: clean-exit-no-Shutdown path doesn't trigger,
  defensive defer ln.Close() aspirational, etc.

Verification:
- go build ./cmd/...  exit 0
- go vet ./...         clean
- ./scripts/d1_smoke.sh  D1 acceptance gate: PASSED
- 3-lineage code review · 14 findings · 7 fixed · 0 deferred · 5
  accepted with rationale

Total D1 review coverage across the phase:
- 3 doc-review passes (Opus + Kimi + Qwen) — 13 findings, 10 fixed
- 1 runtime smoke — 1 finding (port 3100 collision), fixed
- 1 code-review parallel pass — 14 findings, 7 fixed
- 1 code-review second pass (Opus) — 1 actionable, fixed
- Cumulative: 29 findings · 19 fixed inline · 5 accepted · 5 deferred

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/shared/config.go

@@ -6,7 +6,10 @@
 package shared
 
 import (
+	"errors"
 	"fmt"
+	"io/fs"
+	"log/slog"
 	"os"
 
 	"github.com/pelletier/go-toml/v2"
@@ -71,13 +74,21 @@ func DefaultConfig() Config {
 // the file doesn't exist, returns DefaultConfig. Any decode error is
 // fatal (we don't want a misconfigured service silently falling back
 // to defaults — that's the kind of bug you find at 2am).
+//
+// Per Opus + Qwen WARN #3: when path WAS given but the file is
+// missing, log a warning so silent default-fallback doesn't hide
+// misconfiguration. Empty path is fine (caller didn't ask for a
+// file); non-empty + missing is suspicious.
 func LoadConfig(path string) (Config, error) {
 	cfg := DefaultConfig()
 	if path == "" {
 		return cfg, nil
 	}
 	b, err := os.ReadFile(path)
-	if os.IsNotExist(err) {
+	if errors.Is(err, fs.ErrNotExist) {
+		slog.Warn("config file not found, using defaults",
+			"path", path,
+			"hint", "create the file or pass -config /path/to/lakehouse.toml")
 		return cfg, nil
 	}
 	if err != nil {