asyncpoll: refactor Sectigo / Entrust / GlobalSign to bounded polling (Phase 2)

Phase 2 of the #5 acquisition-readiness fix from the 2026-05-01 issuer
coverage audit. Phase 1 (commit 593210f) shipped the shared asyncpoll
package and refactored DigiCert as the reference. This commit applies
the same pattern to the remaining three async-CA connectors and adds
the operator-facing docs.

Per-connector refactors:

- Sectigo (sectigo.go): GetOrderStatus now wraps pollEnrollmentOnce in
  asyncpoll.Poll. The collectNotReady sentinel (cert approved by SCM
  but not yet retrievable from the collect endpoint) maps to
  StillPending and rides the backoff schedule rather than the prior
  "return pending immediately" branch. Added isPermanentStatusError
  helper to distinguish transient HTTP errors (5xx / 429 / network)
  from permanent ones (4xx / parse failure) — the wrapped checkStatus
  errors get triaged at the poll closure boundary.

- Entrust (entrust.go): GetOrderStatus wraps pollEnrollmentOnce. The
  AWAITING_APPROVAL status maps to StillPending; operators using
  approval-pending workflows where humans approve enrollments should
  bump CERTCTL_ENTRUST_POLL_MAX_WAIT_SECONDS to 86400 (24h) so a
  single scheduler tick can wait through the approval window. The
  default 10-minute deadline matches the other three connectors.

- GlobalSign (globalsign.go): GetOrderStatus wraps pollCertificateOnce.
  GlobalSign tracks orders by serial number rather than order ID, but
  the polling shape is identical to the other three. Status-code
  triage matches DigiCert: 4xx (not 429) is permanent, 5xx / 429 /
  network is transient.

Per-connector Config field added:
- DigiCert.PollMaxWaitSeconds (env CERTCTL_DIGICERT_POLL_MAX_WAIT_SECONDS)
- Sectigo.PollMaxWaitSeconds (env CERTCTL_SECTIGO_POLL_MAX_WAIT_SECONDS)
- Entrust.PollMaxWaitSeconds (env CERTCTL_ENTRUST_POLL_MAX_WAIT_SECONDS)
- GlobalSign.PollMaxWaitSeconds (env CERTCTL_GLOBALSIGN_POLL_MAX_WAIT_SECONDS)

internal/config/config.go env-var loaders updated for all four. Default
is 600 seconds (10 minutes); zero falls back to the asyncpoll package
default.

Test-helper updates: every existing test that exercises the pending
branch (collectNotReady, AWAITING_APPROVAL, status="pending", etc.)
now sets PollMaxWaitSeconds=1 in its Config so the test doesn't block
on the production-default 10-minute deadline. Tests that exercise
permanent-error branches (404, 401, malformed JSON, etc.) continue
to return immediately.

Test sites updated:
- buildSectigoConnector helper + GetOrderStatus_CollectNotReady test
- buildEntrustConnector helper + GetOrderStatus_Pending test
- buildGlobalsignConnector helper + GetOrderStatus_Pending test +
  the GetHTTPClient_NoMTLSCertPaths test (network failure now rides
  the backoff schedule rather than returning immediately)

Documentation:
- docs/async-polling.md: new operator reference covering the backoff
  schedule, status-code triage, the four env vars, failure modes, and
  where the implementation lives. Audit blocker citation included.
- docs/connectors.md: per-issuer sections for DigiCert, Sectigo,
  Entrust, GlobalSign each gain the PollMaxWaitSeconds env var row
  and a cross-link to async-polling.md.

Lint cleanup: simplified the isPermanentStatusError branch to satisfy
staticcheck S1008 (single-line return for a final boolean check).

Verified locally:
- gofmt -l . clean
- go vet ./... clean
- staticcheck ./... clean
- golangci-lint run --timeout 5m ./... → 0 issues
- go test -short -count=1 across all 4 connector packages + config + asyncpoll: green

Audit reference: cowork/issuer-coverage-audit-2026-05-01/RESULTS.md
Top-10 fix #5 — Phase 2.

docs/connectors.md

@@ -436,8 +436,9 @@ The DigiCert connector integrates with DigiCert's CertCentral REST API for order
 | `CERTCTL_DIGICERT_ORG_ID` | — | DigiCert organization ID |
 | `CERTCTL_DIGICERT_PRODUCT_TYPE` | `ssl_basic` | Certificate product (e.g., `ssl_basic`, `ssl_plus`, `ssl_ev`) |
 | `CERTCTL_DIGICERT_BASE_URL` | `https://www.digicert.com/services/v2` | DigiCert API base URL |
+| `CERTCTL_DIGICERT_POLL_MAX_WAIT_SECONDS` | `600` | Bounded-polling deadline for `GetOrderStatus`. See [docs/async-polling.md](async-polling.md). |
 
-The connector submits certificate orders to DigiCert's `/order/certificate/create` API. DV certificates may issue immediately; OV/EV certificates require validation (handled by DigiCert) and poll-based completion. The connector periodically checks order status via `/order/certificate/{order_id}` until the certificate is available.
+The connector submits certificate orders to DigiCert's `/order/certificate/create` API. DV certificates may issue immediately; OV/EV certificates require validation (handled by DigiCert) and poll-based completion. `GetOrderStatus` runs bounded internal polling (5s/15s/45s/2m/5m capped, ±20% jitter, default 10-minute deadline) — see [async-polling.md](async-polling.md).
 
 **Authentication:** API key passed via `X-DC-DEVKEY` header, with organization ID in request body.
 
@@ -460,8 +461,9 @@ The Sectigo connector integrates with Sectigo Certificate Manager's REST API for
 | `CERTCTL_SECTIGO_CERT_TYPE` | — | Certificate type ID (integer, from `/ssl/v1/types`) |
 | `CERTCTL_SECTIGO_TERM` | `365` | Certificate validity in days |
 | `CERTCTL_SECTIGO_BASE_URL` | `https://cert-manager.com/api` | Sectigo API base URL |
+| `CERTCTL_SECTIGO_POLL_MAX_WAIT_SECONDS` | `600` | Bounded-polling deadline for `GetOrderStatus`. The `collectNotReady` sentinel (cert approved but not yet retrievable) rides the same backoff schedule. See [docs/async-polling.md](async-polling.md). |
 
-The connector submits certificate enrollments to Sectigo's `/ssl/v1/enroll` API. DV certificates may issue immediately; OV/EV certificates require validation (handled by Sectigo) and poll-based completion. The connector periodically checks enrollment status via `/ssl/v1/{sslId}` and downloads the PEM bundle via `/ssl/v1/collect/{sslId}/pem` when issued.
+The connector submits certificate enrollments to Sectigo's `/ssl/v1/enroll` API. DV certificates may issue immediately; OV/EV certificates require validation (handled by Sectigo) and poll-based completion. `GetOrderStatus` runs bounded internal polling — see [async-polling.md](async-polling.md).
 
 **Authentication:** Three custom headers on every request — `customerUri`, `login`, and `password`.
 
@@ -566,6 +568,7 @@ Entrust CA Gateway REST API with mutual TLS (mTLS) client certificate authentica
 | `CERTCTL_ENTRUST_CLIENT_KEY_PATH` | Yes | — | Path to mTLS client private key PEM |
 | `CERTCTL_ENTRUST_CA_ID` | Yes | — | Certificate Authority ID (from `GET /certificate-authorities`) |
 | `CERTCTL_ENTRUST_PROFILE_ID` | No | — | Optional enrollment profile ID |
+| `CERTCTL_ENTRUST_POLL_MAX_WAIT_SECONDS` | No | `600` (10m) | Bounded-polling deadline for `GetOrderStatus`. Approval-pending workflows where humans approve enrollments should bump to `86400` (24h) so a single tick can wait through the approval window. See [docs/async-polling.md](async-polling.md). |
 
 **Authentication:** Mutual TLS — the client certificate and key are loaded via `tls.LoadX509KeyPair()` and attached to the HTTP transport. No API key or token required.
 
@@ -587,6 +590,7 @@ GlobalSign Atlas High Volume CA REST API with dual authentication: mTLS for the
 | `CERTCTL_GLOBALSIGN_CLIENT_CERT_PATH` | Yes | — | Path to mTLS client certificate PEM |
 | `CERTCTL_GLOBALSIGN_CLIENT_KEY_PATH` | Yes | — | Path to mTLS client private key PEM |
 | `CERTCTL_GLOBALSIGN_SERVER_CA_PATH` | No | system trust store | PEM bundle used to verify the Atlas API server certificate. Set this for private/lab Atlas deployments whose server TLS chain is not in the host's default trust bundle. |
+| `CERTCTL_GLOBALSIGN_POLL_MAX_WAIT_SECONDS` | No | `600` (10m) | Bounded-polling deadline for `GetOrderStatus`. GlobalSign tracks orders by serial number rather than order ID; the polling shape is identical. See [docs/async-polling.md](async-polling.md). |
 
 **Authentication:** Dual — mTLS client certificate for TLS handshake plus `X-API-Key` and `X-API-Secret` headers on every request.