fix: produce valid listener names for wildcard and unusual DNS names

A DNS name like *.home.hrajfrisbee.cz put "*" into the listener name; the
API server rejected the patch, which blocked every certificate on that
Gateway.

- lowercase the DNS part, spell "*" as "wildcard", map other characters
  outside [a-z0-9] to "-"
- names over 253 chars are cut and get a hash suffix instead of a blind cut
- names that were valid before are unchanged

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

docs/flows.md

@@ -325,19 +325,22 @@ The comparison is done via a name-keyed map (`listenerMap`, `patch.go:118`), so
 
 ## 7. Listener Naming and Sanitization
 
-`listenerNameFor` (`patch.go:143`):
+`listenerNameFor` and `sanitizeDNSName` (`patch.go`):
 
 ```
 input:  prefix="auto-"  certName="my-app-cert"  dnsName="app.example.com"
 
-step 1: replace every "." with "-"
+step 1: sanitize the DNS name
+        lowercase; "*" ──► "wildcard"; every other character outside
+        [a-z0-9] ──► "-"; trim leading and trailing "-"
         "app.example.com"  ──►  "app-example-com"
 
 step 2: concatenate
         "auto-" + "my-app-cert" + "-" + "app-example-com"
         ──►  "auto-my-app-cert-app-example-com"
 
-step 3: if len > 253 bytes: name = name[:253]   (hard byte slice)
+step 3: if len > 253: cut to 244, trim trailing "-" and ".", append
+        "-" + first 8 hex chars of sha256(full name)
 ```
 
 Example outputs for a cert with two DNS names:
@@ -345,9 +348,9 @@ Example outputs for a cert with two DNS names:
 | `dnsName` | listener `Name` |
 |-----------|-----------------|
 | `app.example.com` | `auto-my-app-cert-app-example-com` |
-| `*.example.com` | `auto-my-app-cert-*-example-com` |
+| `*.example.com` | `auto-my-app-cert-wildcard-example-com` |
 
-The second entry is a risk: `*` is not valid in a Gateway API `SectionName` (which must match RFC 1123). The API server will reject the patch and the reconciler will requeue forever (see §10, item 7).
+The listener `Hostname` keeps the original DNS name, wildcard included.
 
 The sanitization is also lossy: `a.b.com` and `a-b-com` produce the same result. If a certificate lists both, two listeners with the same name are appended; the API server rejects the patch (listener names must be unique), so no listener on that Gateway is updated.
 
@@ -490,9 +493,9 @@ Branch (F) of Reconcile treats all Gateway `Get` errors the same (including `Not
 `ctrl.NewManager` at `main.go:50` does not set `LeaderElection: true`. The `deploy/deployment_gateway-cert-operator.yaml` runs `replicas: 1` which makes this safe today. Scaling to multiple replicas without enabling leader election would result in concurrent Gateway patches.
 
 **7. `listenerNameFor` edge cases**
-- **Wildcard hostnames**: `*.example.com` produces `SectionName` `auto-…-*-example-com`. The `*` character is not valid in an RFC 1123 label; the Gateway API server will reject the Patch, causing an error-retry loop.
-- **Collisions after sanitization**: `a.b.com` and `a-b-com` produce identical sanitized names. The same happens across certificates (cert `a` with `b-c.com` and cert `a-b` with `c.com`) and across namespaces, since the name omits the cert namespace. Both listeners are appended and the API server rejects the patch for the whole Gateway.
-- **Truncation at 253 bytes**: `patch.go:147` slices on bytes, not runes (safe for ASCII DNS names). Two DNS names sharing the first 253 characters after sanitization will map to the same listener name.
+- **Wildcard hostnames** (fixed): `*` used to end up in the listener name and the API server rejected the patch. It is now spelled out as `wildcard`.
+- **Collisions after sanitization**: `a.b.com` and `a-b-com` produce identical sanitized names, as do `*.x.com` and `wildcard.x.com`. The same happens across certificates (cert `a` with `b-c.com` and cert `a-b` with `c.com`) and across namespaces, since the name omits the cert namespace. Both listeners are appended and the API server rejects the patch for the whole Gateway.
+- **Truncation at 253 bytes** (fixed): long names are cut and get a hash of the full name appended, so they stay valid and distinct.
 
 **Dead symbols in `patch.go`**
 `gatewayGroup` and `gatewayKind` are declared at `patch.go:16-17` but never referenced. They can be removed without effect.

docs/plans-executions/2026-10-08-2046-listener-name-sanitize.md

@@ -3,7 +3,32 @@
 Plan: `docs/plans/2026-10-08-2046-listener-name-sanitize.md`
 
 - [x] Step 0 — Save and commit the plan
-- [ ] Step 1 — Regression tests first
-- [ ] Step 2 — Fix
-- [ ] Step 3 — Docs
+- [x] Step 1 — Regression tests first
+- [x] Step 2 — Fix
+- [x] Step 3 — Docs
 - [ ] Step 4 — Ship
+
+## Steps 1–3 — Tests, fix, docs
+
+Tests were written first and failed on the old code (wildcard, uppercase, `_`,
+trailing dot, long names), then passed after the change to `listenerNameFor`.
+
+```
+$ go test -race -run 'TestListenerNameFor|TestBuildListeners' -v ./internal/gateway/
+--- PASS: TestListenerNameFor_validSectionName/wildcard_label_is_spelled_out
+--- PASS: TestListenerNameFor_longNames
+--- PASS: TestBuildListenersFromCertificates_wildcard
+$ make check
+ok  .../internal/gateway  coverage: 98.6% of statements
+```
+
+Deviations from the plan:
+
+- A trailing `-` or `.` is trimmed from the whole name, not only from the DNS part,
+  so a DNS name that sanitizes to nothing cannot leave the name ending in `-`.
+- One extra case: a trailing dot (`app.example.com.`) is dropped.
+- Steps 1–3 are one commit, since the tests do not pass without the fix.
+
+Worth noting: names that were valid before are unchanged, so existing listeners are
+not renamed. Not verified against a cluster; the production case is covered by the
+test using the exact cert and DNS name from the error log.