Fix distributed transaction manager namespace compile regression on develop

[Copilot]

Target Version (Required)

Target Version: [Unreleased]

This is a build-stability fix for the develop branch and does not introduce new product behavior.

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Description

The develop CI build was failing in the distributed transaction path because the out-of-class definitions for DistributedTransactionManager were not being parsed in the intended namespace scope. This change restores correct compilation context without altering runtime behavior or public interfaces.

• Root cause: the transaction manager implementation was missing an explicit namespace reopen at the definition site, which broke the build for the distributed transaction component.
• Change: updated src/transaction/distributed_transaction_manager.cpp to reopen themis::transaction before the class member definitions.
• Impact: the distributed transaction manager now compiles correctly again, restoring build health for the develop branch with no functional or API changes.

Linked Issues

• CI build health on develop

Type of Change

• Bug fix (non-breaking)
• New feature (non-breaking)
• Refactoring (non-breaking)
• Documentation
• Breaking change (requires MAJOR version bump — see VERSIONING.md)
• Security fix
• Other:

Breaking Change Checklist

• MAJOR version bump planned in VERSION and CMakeLists.txt
• Migration guide added in docs/migration/
• Announcement prepared for GitHub Discussions (≥ 2 weeks before release)
• CHANGELOG ### Removed / ### Changed section updated

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• Benchmarks run (if performance-sensitive change)

Security Tiering Impact (Required for Runtime Changes)

• Impacted tier(s):

  • T0 Trusted Core
  • T1 Security & Platform Services
  • T2 Data Plane Engines
  • T3 Interface & Protocol Edge
  • T4 Managed Extension Runtime
  • T5 Plugin Boundary
  • N/A (docs-only / non-runtime)

• Trust-boundary crossings documented in PR description (example: T3 -> T2, T5 -> T4 brokered call)

• Boundary controls validated for affected T3/T4/T5 paths (AuthN/AuthZ, validation, rate limits, audit)

• Boundary-focused tests added/updated or explicit N/A rationale provided

• If trust level/privilege increased, security maintainer approval is attached

📚 Research & Knowledge (wenn applicable)

• Diese PR basiert auf wissenschaftlichen Paper(s) oder Best Practices?
  • Falls JA: Research-Dateien in /docs/research/ angelegt?
  • Falls JA: Im Modul-README unter "Wissenschaftliche Grundlagen" verlinkt?
  • Falls JA: In /docs/research/implementation_influence/ eingetragen?

Relevante Quellen:

• Paper:
• Best Practice:
• Architecture Decision:

AI-Generated Code (KI-generierter Code)

• Symbol-Referenzen mit GetSymbolReferences_CppTools geprüft (siehe .github/instructions/cpp-language-service-tools.instructions.md)
• Keine rohen Pointer und kein new/delete ohne explizites Review eingeführt
• RAII und Exception-Safety für neue/angepasste Pfade geprüft
• Keine unnötig komplexen KI-Abstraktionen eingeführt
• Performance-Metriken geprüft, falls Hotpath betroffen

AI Review Workflow (Required for AI-assisted PRs)

• Findings-first review performed with .github/prompts/pr-diff-findings-review.prompt.md
• Security hardening review performed for security-sensitive/runtime changes with .github/prompts/security-hardening-review.prompt.md (or N/A documented)
• API impact review performed for API/contract changes with .github/prompts/api-change-impact-review.prompt.md (or N/A documented)
• All Critical/High findings are resolved or explicitly accepted with rationale in PR description
• Residual risks and follow-up actions documented in PR description
• Severity policy applied according to .github/copilot/REVIEW_SEVERITY_POLICY.md

High-Finding Exception Record (only if High is accepted)

• High-finding exception claimed in this PR

• Finding reference:

• Maintainer approver:

• Mitigation in current release:

• Target fix milestone:

• Tracking issue:

• Validation evidence:

Release Readiness Gate (Required for release-scoped changes)

• Release readiness reviewed with .github/prompts/release-readiness-check.prompt.md for branch transition scope
• Branch governance validated against BRANCHING_STRATEGY.md and RELEASE_STRATEGY.md
• Versioning/changelog impact validated against VERSIONING.md and CHANGELOG.md

Checklist

• Code follows project style guidelines (clang-format / clang-tidy)
• Self-review completed
• Documentation updated (if needed)
• CHANGELOG.md updated under [Unreleased]
• No new warnings introduced
• Security-sensitive paths reviewed by security maintainer (if applicable)

Scanner and IntelliSense Gates

• IntelliSense/Compiler: no new errors in changed files
• clang-tidy/cppcheck: no new high-risk findings in changed files
• Gap Scanner: no new critical findings in categories security, input_validation, query_correctness, distributed_consistency, concurrency, memory
• Gap Scanner: no new high findings in the same categories (or explicitly approved)
• Gap Scanner delta report attached (baseline vs current), not only absolute totals
• New unknown scanner findings triaged (fixed, re-categorized, or justified)

• Fixes [CI] Build status tracker — develop #6231

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