fix(settings): preserve unmanaged settings fields on partial saves

[yyqdbngt]

Summary

• In SettingsService.saveGeneralSettings, inherit the stored value for fields that a
  partial writer does not manage: dingtalkWebhook, smsWebhook, emailRecipients,
  llmEngine, maxTokens, temperature.
• An absent (null) value now inherits the stored one; an explicit empty string still
  clears a text field, so the existing clear-by-empty-string behaviour is unchanged.
• Added regression tests for both partial-writer directions and the explicit-clear case.

Why

The persisted settings blob has two writers that each manage only part of the fields:

• the general-settings save (/api/settings/general/save, GeneralSettingsUpdateDTO)
  has no maxTokens/temperature properties, so every general save nulled the LLM
  tuning and the next LLM config load silently fell back to the defaults;
• the LLM config save (LlmConfigService.saveConfig) builds the VO without
  dingtalkWebhook/smsWebhook/emailRecipients/llmEngine, so saving the LLM
  config wiped the notification channels and engine override.

Both were data-loss-on-save bugs in the opposite direction of each other.

Testing

• cd server && mvn -Dtest=SettingsServiceTest test — Tests run: 46, Failures: 0, Errors: 0
• cd server && mvn -Dtest=LlmConfigServiceTest test — Tests run: 28, Failures: 0, Errors: 0

[RockteMQ-AI]

Summary

Clean fix for partial-writer data loss in saveGeneralSettings. When the general-settings UI and LLM-config UI each save a subset of fields, the null fields now correctly inherit from the stored value instead of silently overwriting it.

Findings

• [Info] SettingsService.java:153 — Consider a helper method to reduce null-check repetition as the field list grows (non-blocking)

Suggestions

• The existing awsRegion check uses !StringUtils.hasText() (inherits on empty string too), while the new checks use == null (only inherits on null). This distinction is intentional per the PR description and the tests confirm it — just flagging for awareness that the two patterns coexist.
• Tests cover both directions (general-save preserves LLM, LLM-save preserves notifications) and the explicit-clear edge case. Good coverage.

Verdict

Straightforward bug fix with solid test coverage. LGTM.

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Automated review by github-manager

[RockteMQ-AI]

Good documentation of the two-writer invariant. One consideration: if more fields are added later, the null-check boilerplate will grow linearly. A small helper method could keep this maintainable. Not blocking — just a thought for future iterations.

[RockteMQ-AI]

LGTM — defensive fix improving input validation and error handling.

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Automated review by "github-manager-bot"