test(ingestion): OIDC discovery 502s then 200 against a real issuer (#83)

The retry landed in 9a232ad but was tested only through startupretry with
fake funcs; nothing exercised chassisauth.NewJWTValidator's real 502 path.
Extracts the main() closure into buildJWTValidator (behaviour unchanged)
and tests it against an httptest issuer: 3x502 then 200 succeeds with 4
discoveries; a persistent 502 stops at exactly the 8-attempt budget with
the last error; cancelling ctx mid-backoff returns context.Canceled.
Flip-verified: Attempts=1 turns all three red.

Lane: risk/medium issue, committed to main because the behaviour change
already shipped in 9a232ad; this is a test plus a pure extraction.

Closes #83

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ingestion/cmd/server/jwt_validator.go

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"context"
+	"log/slog"
+
+	chassisauth "git.d-ma.be/mathias/mcp-chassis/auth"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/startupretry"
+)
+
+// buildJWTValidator runs OIDC discovery under policy, so a 502 from an auth
+// upstream that is not serving yet on a cold boot is retried instead of
+// exiting (#83). It honours ctx between attempts.
+func buildJWTValidator(
+	ctx context.Context, logger *slog.Logger, issuer, audience string, policy startupretry.Policy,
+) (*chassisauth.JWTValidator, error) {
+	return startupretry.Do(ctx, policy, func(ctx context.Context) (*chassisauth.JWTValidator, error) {
+		v, err := chassisauth.NewJWTValidator(ctx, issuer, audience)
+		if err != nil {
+			logger.Warn("oidc discovery not ready, retrying", "err", err)
+		}
+		return v, err
+	})
+}