fix(settings): preserve default forwarding keyword rewrites

[i1hwan]

Summary

• change forwarding keyword settings semantics so saved config overlays the default safety rewrite rules instead of replacing them outright
• keep default Claude OAuth lexical rewrites active when persisted settings contain empty arrays, invalid entries, or only partial overrides
• add regression coverage proving saved settings can customize matching rules without silently disabling the remaining defaults

Verification

• node --import tsx/esm --test tests/unit/translator-openai-to-claude.test.mjs
• npx eslint open-sse/config/forwardingKeywordRules.ts src/app/api/settings/tests/forwarding-keywords.test.ts tests/unit/translator-openai-to-claude.test.mjs
• npm run typecheck:core
• manual API QA confirmed empty saved settings still rewrite background_cancel -> background_stop and background_output <directories>src/</directories> -> background_result directories:\nsrc/

[Copilot]

Pull request overview

This PR adjusts forwarding keyword settings so persisted configurations overlay the default safety/Claude OAuth rewrite rules instead of replacing them, preventing defaults from being silently disabled by empty/partial saved configs.

Changes:

• Added merge logic so lane rules keep defaults unless a saved rule explicitly overrides a matching default.
• Updated normalization behavior and expanded unit coverage around empty arrays, partial overrides, and invalid entries.
• Updated /api/settings/forwarding-keywords tests to assert the effective (normalized) config retains defaults.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
tests/unit/translator-openai-to-claude.test.mjs	Adds regression tests ensuring normalization and runtime rewriting keep default rules active with empty/partial saved config.
src/app/api/settings/tests/forwarding-keywords.test.ts	Updates API tests to validate effective config preserves defaults and supports partial overrides.
open-sse/config/forwardingKeywordRules.ts	Implements rule-merging in normalization so saved settings overlay (not replace) default forwarding keyword rules.

Comments suppressed due to low confidence (1)

open-sse/config/forwardingKeywordRules.ts:144

• Per repo PR gate, please run npm run test:coverage for this change (it modifies production code under open-sse/) and ensure coverage meets the minimum thresholds; consider adding the resulting coverage summary to the PR description/check output so reviewers can verify the gate passed.

export function normalizeForwardingKeywordConfig(value: unknown): ForwardingKeywordConfig {
  const normalized = cloneForwardingKeywordConfig(DEFAULT_FORWARDING_KEYWORD_CONFIG);
  if (!value || typeof value !== "object") return normalized;

  const rawConfig = value as Record<string, unknown>;
  for (const lane of Object.keys(DEFAULT_FORWARDING_KEYWORD_CONFIG) as ForwardingKeywordLane[]) {
    const rawLane = rawConfig[lane];
    if (!rawLane || typeof rawLane !== "object") continue;

    const rawLaneConfig = rawLane as Record<string, unknown>;
    const toolNameOverrides = Array.isArray(rawLaneConfig.toolNames)
      ? rawLaneConfig.toolNames.map(normalizeKeywordRule).filter(Boolean)
      : [];
    const textOverrides = Array.isArray(rawLaneConfig.text)
      ? rawLaneConfig.text.map(normalizeKeywordRule).filter(Boolean)
      : [];
    const tagOverrides = Array.isArray(rawLaneConfig.tags)
      ? rawLaneConfig.tags.map(normalizeTagRule).filter(Boolean)
      : [];

    normalized[lane] = {
      toolNames: mergeKeywordRules(normalized[lane].toolNames, toolNameOverrides),
      text: mergeKeywordRules(normalized[lane].text, textOverrides),
      tags: mergeTagRules(normalized[lane].tags, tagOverrides),
    };
  }

  return normalized;
}