outline: strict values.schema.json and null-safe hardening

No ingress gate: this chart already gates its Ingress correctly. Two
changes plus one guard the existing gate turned out to need.

1. values.schema.json (#68): additionalProperties: false on every
   chart-owned object level.

2. Null-safety for hardening, probes and resources (#99). All three
   probes keep /_health when rebuilt: it is Outline's only health
   endpoint, and "/" returns 500 as well when the database is down, so
   there is no dependency-free path to fall back to.

3. ingress.domain is required() where the StatefulSet reads it. It feeds
   the URL env var - Outline's public URL for generated links and the
   OIDC redirect URI - and did so without a guard. With the existing gate
   and no domain it rendered "https://", breaking logins silently. That
   hole predates this change; it now fails loudly.

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

Apart from an added comment, the rendered manifest is unchanged.

outline/templates/_helpers.tpl

@@ -114,3 +114,159 @@ 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 "outline.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 "outline.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.outline.securityContext" can itself be erased.
+*/}}
+{{- define "outline.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 (issue #99).
+
+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.
+
+All three probes use /_health on purpose: it is the only health endpoint
+Outline offers, and "/" returns 500 as well when the database is down, so
+there is no dependency-free alternative to fall back to.
+*/}}
+{{- define "outline.podSecurityContext" -}}
+{{- $given := (fromYaml (include "outline.subBlock" (dict "block" . "key" "pod" "path" "outline.securityContext"))).value -}}
+{{- $defaults := dict
+      "runAsNonRoot" true
+      "runAsUser" 1001
+      "runAsGroup" 1001
+      "fsGroup" 1001
+      "fsGroupChangePolicy" "Always" -}}
+{{- include "outline.defaultedDict" (dict "defaults" $defaults "given" $given "path" "outline.securityContext.pod") -}}
+{{- end -}}
+
+{{- define "outline.containerSecurityContext" -}}
+{{- $given := (fromYaml (include "outline.subBlock" (dict "block" . "key" "container" "path" "outline.securityContext"))).value -}}
+{{- $defaults := dict
+      "allowPrivilegeEscalation" false
+      "readOnlyRootFilesystem" true
+      "runAsNonRoot" true
+      "capabilities" (dict "drop" (list "ALL")) -}}
+{{- include "outline.defaultedDict" (dict "defaults" $defaults "given" $given "path" "outline.securityContext.container") -}}
+{{- end -}}
+
+{{- define "outline.livenessProbe" -}}
+{{- $defaults := dict
+      "httpGet" (dict "path" "/_health" "port" 3000)
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 3 -}}
+{{- include "outline.defaultedDict" (dict "defaults" $defaults "given" . "path" "outline.livenessProbe") -}}
+{{- end -}}
+
+{{- define "outline.readinessProbe" -}}
+{{- $defaults := dict
+      "httpGet" (dict "path" "/_health" "port" 3000)
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 3 -}}
+{{- include "outline.defaultedDict" (dict "defaults" $defaults "given" . "path" "outline.readinessProbe") -}}
+{{- end -}}
+
+{{- define "outline.startupProbe" -}}
+{{- $defaults := dict
+      "httpGet" (dict "path" "/_health" "port" 3000)
+      "periodSeconds" 10
+      "timeoutSeconds" 5
+      "failureThreshold" 30 -}}
+{{- include "outline.defaultedDict" (dict "defaults" $defaults "given" . "path" "outline.startupProbe") -}}
+{{- end -}}
+
+{{/*
+The effective resources block, fed into the resources helper above so that an
+erased "resources:" still yields the chart's requests and computed limits
+instead of a container without any resource accounting.
+*/}}
+{{- define "outline.effectiveResources" -}}
+{{- $defaults := dict
+      "limitFactor" 3
+      "requests" (dict "cpu" 0.1 "memory" "512Mi" "ephemeralStorage" "10Mi") -}}
+{{- $merged := fromYaml (include "outline.defaultedDict" (dict "defaults" $defaults "given" . "path" "outline.resources")) -}}
+{{- include "outline.resources" $merged -}}
+{{- end -}}

outline/templates/outline.sfs.yaml

@@ -18,7 +18,7 @@ spec:
     spec:
       automountServiceAccountToken: false
       securityContext:
-        {{- toYaml .Values.outline.securityContext.pod | nindent 8 }}
+        {{- include "outline.podSecurityContext" .Values.outline.securityContext | nindent 8 }}
       containers:
         - name: {{ .Release.Name }}-{{ .Chart.Name }}-sfs
           image: "outlinewiki/outline:{{ .Chart.AppVersion }}"
@@ -26,8 +26,12 @@ spec:
           env:
             - name: PORT
               value: "3000"
+            # ingress.domain is not a pure Ingress value: it is also Outline's
+            # public URL, used for generated links and the OIDC redirect URI,
+            # so it stays required even when the Ingress is switched off (an
+            # empty value would render "https://" and break logins silently).
             - name: URL
-              value: "https://{{ .Values.ingress.domain }}"
+              value: "https://{{ required "A Domain/Host must be provided (ingress.domain)" .Values.ingress.domain }}"
             - name: SECRET_KEY
               valueFrom:
                 secretKeyRef:
@@ -100,15 +104,15 @@ spec:
               protocol: TCP
               name: http
           livenessProbe:
-            {{- toYaml .Values.outline.livenessProbe | nindent 12 }}
+            {{- include "outline.livenessProbe" .Values.outline.livenessProbe | nindent 12 }}
           readinessProbe:
-            {{- toYaml .Values.outline.readinessProbe | nindent 12 }}
+            {{- include "outline.readinessProbe" .Values.outline.readinessProbe | nindent 12 }}
           startupProbe:
-            {{- toYaml .Values.outline.startupProbe | nindent 12 }}
+            {{- include "outline.startupProbe" .Values.outline.startupProbe | nindent 12 }}
           resources:
-            {{- include "outline.resources" .Values.outline.resources | nindent 12 }}
+            {{- include "outline.effectiveResources" .Values.outline.resources | nindent 12 }}
           securityContext:
-            {{- toYaml .Values.outline.securityContext.container | nindent 12 }}
+            {{- include "outline.containerSecurityContext" .Values.outline.securityContext | nindent 12 }}
           volumeMounts:
             - mountPath: "/outline-data/data"
               name: outline-data