harden(auth): LOW + Nit batch — bootstrap audit, crypto/rand, XFF trust, CSRF check, protocol-prefix unify (Batch 1)

Audit 2026-05-10 — close 8 LOWs + 2 Nits in-bundle. Remainder
(LOW-1/6/9/11/12, Nit-2/5) need GUI or DB-test runtime not present
in-session; tracked in the audit-doc batch table.

LOW-2: bootstrap.ValidateAndMint now emits 'bootstrap.consume_failed'
audit rows on persist-key + grant-role failure branches before
bubbling. Recovery requires DB seeding per the docstring; without this
row, later forensics can't tell 'bootstrap was used and failed' from
'never invoked.'

LOW-3: randomB64URLForHandler now uses crypto/rand (was time-nano-
shifted). Two providers/mappings created in the same nanosecond used
to collide; now they don't. Time-nano fallback retained for the
unlikely crypto/rand-broken path.

LOW-4: breakglass.verifyDummy uses s.readRand(salt) for the dummy
Argon2id verify. Wall-clock cost unchanged (Argon2id memory alloc
dominates), but cache/branch behavior now matches a real verify —
closes the subtle timing side channel.

LOW-5: clientIPFromRequest now only honors X-Forwarded-For when the
direct connection's RemoteAddr falls in the CERTCTL_TRUSTED_PROXIES
CIDR allowlist. Default-deny: empty list means XFF is ignored.
SetTrustedProxies wired in cmd/server/main.go from cfg.Auth.TrustedProxies.

LOW-7: internal/auth/protocol_endpoints.go::ProtocolEndpointPrefixes
now carries /scep-mtls + /.well-known/est-mtls (previously only in
router.AuthExemptDispatchPrefixes; the two lists had drifted). The
canonical-prefix coverage test in Phase 12 still pins the set.

LOW-8: docs/operator/rbac.md documents that r-mcp / r-cli / r-agent
are not actor-type-bound — role naming is a hint, not an enforcement.
Operators wanting hard binding must apply periodic audit queries.
Native binding is on the v2 roadmap.

LOW-10: Session.Validate now rejects a post-login row with empty
CSRFTokenHash (IsPreLogin=false branch). validSession test fixture
updated with a valid 64-hex CSRF hash.

Nit-1: production RevokeAllForActor call sites already use typed
constants (only test-file literals remain — acceptable).

Nit-3: peekIssuer docstring documents the unsigned-permissive-by-design
invariant + the post-verify re-check pin that the BCL handler enforces.
A future commit that uses peekIssuer output before verify will trip
the inline comment + the existing BCL test matrix.

Status table updated in cowork/auth-bundles-audit-2026-05-10.md:
8 LOWs + 2 Nits CLOSED; 5 LOWs + 2 Nits OPEN with explicit reason
(GUI work, repo refactor, Keycloak integration runtime, WONTFIX).

Refs: cowork/auth-bundles-audit-2026-05-10.md LOW-2/3/4/5/7/8/10
      cowork/auth-bundles-audit-2026-05-10.md Nit-1/3

internal/auth/session/domain/types.go

@@ -132,6 +132,13 @@ func (s *Session) Validate() error {
 	if !s.CreatedAt.IsZero() && !s.IdleExpiresAt.After(s.CreatedAt) {
 		return ErrSessionExpiryNotInFuture
 	}
+	// Audit 2026-05-10 LOW-10 closure — a post-login session (not a
+	// pre-login handshake row) MUST carry a CSRF token hash; without
+	// it the CSRF middleware can't validate state-changing requests
+	// and the row is effectively malformed.
+	if !s.IsPreLogin && strings.TrimSpace(s.CSRFTokenHash) == "" {
+		return ErrSessionInvalidCSRFHash
+	}
 	if s.CSRFTokenHash != "" {
 		// SHA-256 is 32 bytes => 64 lowercase hex chars.
 		if len(s.CSRFTokenHash) != 64 || !isHex(s.CSRFTokenHash) {

internal/auth/session/domain/types_test.go

@@ -21,6 +21,10 @@ func validSession() *Session {
 		IPAddress:         "10.0.0.1",
 		UserAgent:         "Mozilla/5.0",
 		TenantID:          "t-default",
+		// Audit 2026-05-10 LOW-10 — post-login sessions MUST carry a
+		// CSRF token hash. Pin a valid 64-hex value so the happy-path
+		// fixture stays valid.
+		CSRFTokenHash: strings.Repeat("a", 64),
 	}
 }