feat: add mail_sender_strategy policy to send notifications as the requester

[maia-andre]

Pull Request Description

Implements the mail_sender_strategy policy described in #7954 so LibreSign can send signature request notification emails either through the system mailer (current behavior) or through the mail account of the person who requested the signature.

Backend

• New MailSenderStrategyPolicy (lib/Service/Policy/Provider/MailSenderStrategy/), registered in PolicyProviders. Values: system (default) and requester. System scope only in this first step (supportedScopes: ['system'], no user preference, no group delegation), since per-user choice is out of scope.
• MailService::notifyUnsignedUser() and notifySignDataUpdated() now resolve the policy for the requester (resolveForUserId() on the file owner, so the same strategy applies to reminders sent from cron, where there is no session user).
• Under requester, the notification is sent through OCP\Mail\Provider\IManager: the service is looked up by the requester's email address (findServiceByAddress()), falling back to the first service of the account that implements IMessageSend. The message reuses the existing IEMailTemplate (renderSubject(), renderHtml(), renderText()), so content and templating are unchanged.
• Fallback to IMailer (identical to the current code path) when there is no mail provider, the requester account is missing, no service can send messages, or provider sending throws. Logging: info for the "not available" cases, warning (with the exception) when provider sending fails. Errors from the final IMailer path keep raising LibresignException as before.

Configuration vs. runtime (follow-up of the review in #7954)

• The requester strategy can only be saved while a mail provider is registered (OCP\Mail\Provider\IManager::has(), independent of any specific app). This uses a new persistence-only hook in the policy framework, IPolicyDefinition::validateValueForPersistence(), called from the PolicyService save paths. Runtime resolution keeps using validateValue(), so an already stored requester value is not silently discarded by DefaultPolicyResolver when the environment changes later; instead MailService falls back at sending time.
• The availability is exposed as meta.mailProviderAvailable (OpenAPI spec and generated types updated) and the Policy Workbench editor disables the requester option with a hint when no provider is available.
• When the strategy is requester and the notification falls back to the system mailer, Reply-To is set to the requester's address, so replies still reach the person who requested the signature. The system strategy is unchanged.

Frontend

• Policy Workbench definition under src/views/Settings/PolicyWorkbench/settings/mail-sender-strategy/ (radio editor with the two strategies), added to the system-behavior category in realDefinitions.ts.

Tests

• MailSenderStrategyPolicyTest: definition, scope restriction, normalization and validation, provider required on save (and stored value still valid at runtime), resolved meta.
• PolicySpecTest: the persistence-only validation hook.
• MailServiceTest: system strategy, successful requester sending (from/to/subject/html/plain), recipient label handling, every fallback path (no provider, unknown requester, missing account, no sendable service, provider failure, fallback failure) and the Reply-To behavior on fallback.
• realDefinitions.spec.ts, mail-sender-strategy/*.spec.ts: workbench card, definition callbacks, model and editor (including the disabled state).

Checks run locally: PHPUnit unit suite, psalm and php-cs-fixer on the changed files, npm run lint, vue-tsc --noEmit, vitest for the Policy Workbench suites.

Manual verification

Devcontainer with Mailpit as the system mailer and no mail provider app installed, so the requester strategy exercises the fallback path end to end.

1. New card in the Policy Workbench (System behavior), default System mailer:

   

2. Rule editor with the two strategies:

   

3. Selecting Requester mail account and saving the system rule:

   

   

4. Card after saving (occ config:app:get libresign mail_sender_strategy → requester):

   

5. Signature request sent through the API with the policy set to requester: the notification is still delivered, through the system mailer, and the fallback is logged at info level:

   

   {"level": 1, "app": "libresign", "message": "No mail provider is available to send the notification as the requester, falling back to the system mailer.", "requester": "admin"}

6. Follow-up of the review: on the same instance (no mail provider), the requester option can no longer be configured. The editor disables it with a hint, and the API rejects it with 400:

   

   POST /ocs/v2.php/apps/libresign/api/v1/policies/system/mail_sender_strategy  {"value":"requester"}
   HTTP 400  {"ocs":{"meta":{"status":"failure","statuscode":400},"data":{"error":"The requester strategy requires an available mail provider"}}}
   

   The screenshots in steps 3–5 were taken before this change; they show the rule saved while the check did not exist yet, which is exactly the "environment changed later" case that the runtime fallback (and now Reply-To) covers.

Related Issue

Fixes #7954

Pull Request Type

• Feature

Pull request checklist

• The policy supports system and requester
• The policy is available in the backend and Policy Workbench
• system preserves the current behavior
• requester attempts provider-based sending
• Falls back to IMailer when no provider, account or sending service is available, or when sending fails
• requester cannot be configured while no mail provider is available (persistence-time check)
• Reply-To set to the requester when falling back to the system mailer
• Applied to notifyUnsignedUser and notifySignDataUpdated
• Tests cover system, successful requester and fallback
• AI-assisted: yes (see commit trailer)

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Files with missing lines	Coverage Δ
...l-sender-strategy/MailSenderStrategyRuleEditor.vue	100.00% <100.00%> (ø)
...cyWorkbench/settings/mail-sender-strategy/model.ts	100.00% <100.00%> (ø)
...ch/settings/mail-sender-strategy/realDefinition.ts	100.00% <100.00%> (ø)
...ttings/PolicyWorkbench/settings/realDefinitions.ts	100.00% <ø> (ø)

... and 208 files with indirect coverage changes

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