matrix-synapse: strict schema, ingress gate and null-safe hardening

Three changes, across both workloads (Synapse StatefulSet and delegation
nginx Deployment).

1. values.schema.json (#68): additionalProperties: false on every
   chart-owned object level, including the whole matrix.delegation block
   with its own contexts, probes and resources.

2. Ingress gate (#93): the Ingress template is wrapped in
   {{- if .Values.ingress.enabled }} and the key is added to values.yaml
   with default true, so behaviour is unchanged.

   The domain checkpoint found a second reader: the delegation nginx
   serves ingress.domain in its /.well-known/matrix/{server,client}
   endpoints, and read it without a guard. Gating alone would therefore
   have published '{"m.server": ":443"}' and base_url "https://" - a
   federation-breaking answer that renders and starts cleanly. Both reads
   are now required(), so that case fails loudly. Only clusterIssuer
   actually becomes unnecessary when the Ingress is off.

3. Null-safety for hardening, probes and resources (#99) for both
   workloads. The rebuilt probes keep each workload's own endpoint:
   Synapse /health, delegation /.well-known/matrix/server - the endpoint
   that workload exists to serve - including its shorter 3s timeout. The
   delegation pod context keeps having no fsGroup, because it mounts no
   volume that needs one.

The nginx checksum/config annotation from #82 is untouched.

storage stays deliberately not null-safe: an erased block yields an
invalid PVC, which is the loud class #99 excludes.

Rendering is byte-identical to 6.0.0, both with the CI values (which
enable delegation) and with the production bundle values.

matrix-synapse/templates/_helpers.tpl

@@ -114,3 +114,227 @@ template-chart is the reference implementation.
 1
 {{- end -}}
 {{- end -}}
+
+{{/*
+Merge a user-supplied values sub-tree onto a dict of chart defaults so that a
+null / empty override falls back to the defaults instead of erasing them.
+
+Input: dict "defaults" <dict> "given" <dict|nil> "path" <string, optional
+values path used in error messages>. Output: YAML of the merged dict (consume
+it with fromYaml).
+
+Why this exists (issue #99): Helm merges values maps recursively, but an
+override key written without children — e.g. a leftover
+
+  securityContext:
+
+after deleting its last remaining sub-key — is YAML null. Where the chart
+defines a default, Helm treats that null as a deletion of the default; the
+template then renders "securityContext: null": no readOnlyRootFilesystem, no
+dropped capabilities, no allowPrivilegeEscalation: false. The workload starts
+and reports healthy while being unhardened, so nothing points at the mistake.
+The same shape erases a probe (it disappears) or the resources block (no
+requests, no computed limits). This helper defines the opposite semantics: an
+empty block means "chart defaults apply".
+
+Rules:
+  - a nil "given" is treated as an empty dict (all defaults apply).
+  - a key whose override value is null keeps the default (nulls never delete).
+  - a key present in both as a map is merged recursively, so a partially
+    filled block only overrides the keys it actually sets.
+  - a scalar override for a key the defaults define as a map is rejected with
+    a message naming the values path, instead of failing later with a template
+    field error.
+  - any other set value wins as given, including an explicit false or 0 —
+    Helm's "default" and sprig's "mergeOverwrite" would both swallow those
+    zero values, hence the explicit kindIs "invalid" nil check.
+  - keys only present in the override are passed through unchanged.
+
+NOTE: like the helpers above, this is duplicated into every chart's
+templates/_helpers.tpl with the chart's name as define prefix, because charts
+in this repo deliberately have no dependencies.
+*/}}
+{{- define "matrix-synapse.defaultedDict" -}}
+{{- $defaults := .defaults | default dict -}}
+{{- $given := .given -}}
+{{- $path := .path | default "value" -}}
+{{- if kindIs "invalid" $given -}}
+{{- $given = dict -}}
+{{- end -}}
+{{- if not (kindIs "map" $given) -}}
+{{- fail (printf "%s must be a mapping or null, got %s (%v)" $path (kindOf $given) $given) -}}
+{{- end -}}
+{{- $out := deepCopy $defaults -}}
+{{- range $key, $value := $given -}}
+{{- if not (kindIs "invalid" $value) -}}
+{{- $default := index $defaults $key -}}
+{{- if and (kindIs "map" $value) (kindIs "map" $default) -}}
+{{- $_ := set $out $key (fromYaml (include "matrix-synapse.defaultedDict" (dict "defaults" $default "given" $value "path" (printf "%s.%s" $path $key)))) -}}
+{{- else if kindIs "map" $default -}}
+{{- fail (printf "%s.%s must be a mapping or null, got %s (%v)" $path $key (kindOf $value) $value) -}}
+{{- else -}}
+{{- $_ := set $out $key $value -}}
+{{- end -}}
+{{- end -}}
+{{- end -}}
+{{- toYaml $out -}}
+{{- end -}}
+
+{{/*
+Pick one sub-block out of a values block that may itself be null.
+
+Input: dict "block" <dict|nil> "key" <string> "path" <string>.
+Returns YAML of dict "value" <the sub-block, may be nil>, after rejecting a
+non-mapping block with a message that names the values path. Needed because
+".Values.matrix.securityContext" can itself be erased.
+*/}}
+{{- define "matrix-synapse.subBlock" -}}
+{{- $block := .block -}}
+{{- if kindIs "invalid" $block -}}
+{{- $block = dict -}}
+{{- end -}}
+{{- if not (kindIs "map" $block) -}}
+{{- fail (printf "%s must be a mapping or null, got %s (%v)" .path (kindOf $block) $block) -}}
+{{- end -}}
+{{- toYaml (dict "value" (index $block .key)) -}}
+{{- end -}}
+
+{{/*
+The effective security contexts, probes and resources of BOTH workloads
+(issue #99) - the Synapse StatefulSet and the delegation nginx Deployment.
+
+The defaults below MUST stay in sync with the corresponding blocks in
+values.yaml, which stays the documented, user-facing place for them; this copy
+is only the fallback for the case where an override has erased the block.
+
+Synapse specifics a rebuilt default must not lose:
+  - uid/gid 1000 matches the previous gosu default, so existing PVC data stays
+    accessible. The upstream image only drops privileges itself when started as
+    root; with an explicit non-root runAsUser it runs directly as that user.
+  - the probes hit /health on the named "http" port and set scheme HTTP
+    explicitly.
+  - the startup budget is 10s x 30 = 300s (migrations, cache warmup).
+
+Delegation nginx specifics:
+  - it runs as the image's unprivileged nginx user (uid 101) and its pod
+    context deliberately has NO fsGroup - it mounts no volume that needs one.
+  - its probes hit /.well-known/matrix/server, which is the endpoint the whole
+    workload exists for, with a shorter 3s timeout.
+*/}}
+{{- define "matrix-synapse.podSecurityContext" -}}
+{{- $given := (fromYaml (include "matrix-synapse.subBlock" (dict "block" . "key" "pod" "path" "matrix.securityContext"))).value -}}
+{{- $defaults := dict
+      "runAsNonRoot" true
+      "runAsUser" 1000
+      "runAsGroup" 1000
+      "fsGroup" 1000
+      "fsGroupChangePolicy" "Always" -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" $given "path" "matrix.securityContext.pod") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.containerSecurityContext" -}}
+{{- $given := (fromYaml (include "matrix-synapse.subBlock" (dict "block" . "key" "container" "path" "matrix.securityContext"))).value -}}
+{{- $defaults := dict
+      "allowPrivilegeEscalation" false
+      "readOnlyRootFilesystem" true
+      "runAsNonRoot" true
+      "capabilities" (dict "drop" (list "ALL")) -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" $given "path" "matrix.securityContext.container") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.probeHttpGet" -}}
+{{- dict "path" "/health" "port" "http" "scheme" "HTTP" | toYaml -}}
+{{- end -}}
+
+{{- define "matrix-synapse.livenessProbe" -}}
+{{- $defaults := dict
+      "httpGet" (fromYaml (include "matrix-synapse.probeHttpGet" .))
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 3 -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" . "path" "matrix.livenessProbe") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.readinessProbe" -}}
+{{- $defaults := dict
+      "httpGet" (fromYaml (include "matrix-synapse.probeHttpGet" .))
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 3 -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" . "path" "matrix.readinessProbe") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.startupProbe" -}}
+{{- $defaults := dict
+      "httpGet" (fromYaml (include "matrix-synapse.probeHttpGet" .))
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 30 -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" . "path" "matrix.startupProbe") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.effectiveResources" -}}
+{{- $defaults := dict
+      "limitFactor" 3
+      "requests" (dict "memory" "1Gi" "cpu" "1" "ephemeralStorage" "1Gi") -}}
+{{- $merged := fromYaml (include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" . "path" "matrix.resources")) -}}
+{{- include "matrix-synapse.resources" $merged -}}
+{{- end -}}
+
+{{- define "matrix-synapse.delegation.podSecurityContext" -}}
+{{- $given := (fromYaml (include "matrix-synapse.subBlock" (dict "block" . "key" "pod" "path" "matrix.delegation.securityContext"))).value -}}
+{{- $defaults := dict
+      "runAsNonRoot" true
+      "runAsUser" 101
+      "runAsGroup" 101 -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" $given "path" "matrix.delegation.securityContext.pod") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.delegation.containerSecurityContext" -}}
+{{- $given := (fromYaml (include "matrix-synapse.subBlock" (dict "block" . "key" "container" "path" "matrix.delegation.securityContext"))).value -}}
+{{- $defaults := dict
+      "allowPrivilegeEscalation" false
+      "readOnlyRootFilesystem" true
+      "runAsNonRoot" true
+      "capabilities" (dict "drop" (list "ALL")) -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" $given "path" "matrix.delegation.securityContext.container") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.delegation.probeHttpGet" -}}
+{{- dict "path" "/.well-known/matrix/server" "port" "http" "scheme" "HTTP" | toYaml -}}
+{{- end -}}
+
+{{- define "matrix-synapse.delegation.livenessProbe" -}}
+{{- $defaults := dict
+      "httpGet" (fromYaml (include "matrix-synapse.delegation.probeHttpGet" .))
+      "periodSeconds" 10
+      "timeoutSeconds" 3
+      "failureThreshold" 3 -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" . "path" "matrix.delegation.livenessProbe") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.delegation.readinessProbe" -}}
+{{- $defaults := dict
+      "httpGet" (fromYaml (include "matrix-synapse.delegation.probeHttpGet" .))
+      "periodSeconds" 10
+      "timeoutSeconds" 3
+      "failureThreshold" 3 -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" . "path" "matrix.delegation.readinessProbe") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.delegation.startupProbe" -}}
+{{- $defaults := dict
+      "httpGet" (fromYaml (include "matrix-synapse.delegation.probeHttpGet" .))
+      "periodSeconds" 5
+      "timeoutSeconds" 3
+      "failureThreshold" 30 -}}
+{{- include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" . "path" "matrix.delegation.startupProbe") -}}
+{{- end -}}
+
+{{- define "matrix-synapse.delegation.effectiveResources" -}}
+{{- $defaults := dict
+      "limitFactor" 3
+      "requests" (dict "memory" "64Mi" "cpu" "125m" "ephemeralStorage" "50Mi") -}}
+{{- $merged := fromYaml (include "matrix-synapse.defaultedDict" (dict "defaults" $defaults "given" . "path" "matrix.delegation.resources")) -}}
+{{- include "matrix-synapse.resources" $merged -}}
+{{- end -}}