chore(deps): revert NSec.Cryptography to stable 26.4.0

[ctwoodwa]

Summary

• Reverts NSec.Cryptography from preview 26.1.0-preview.1 to stable 26.4.0 in Directory.Packages.props
• Aligns signal-bridge with shipyard and sunfish, both of which pin 26.4.0 (stable)
• Eliminates a preview crypto dependency from a security-sensitive Bridge comms service (Layer-1 prevention)

Rationale

QM V4 #6 SDK drift recheck (qm-status-2026-05-22T0945Z-v4-item-6-alert-advisory.md) flagged that signal-bridge had regressed NSec.Cryptography to preview while sibling repos track the stable release. NSec is the cryptographic primitives library used in the Bridge key-exchange and message-signing paths. Running preview crypto in production is a security hygiene issue regardless of API stability claims.

Admiral ruling 2026-05-22T13:00Z: revert to 26.4.0. No API changes between the two versions per NuGet history; this is a version-number-only change.

Change

Directory.Packages.props line 31: 26.1.0-preview.1 → 26.4.0

Refs: qm-status-2026-05-22T0945Z-v4-item-6-alert-advisory.md

Test plan

• CI .NET build + test green on signal-bridge
• Verify no NSec.Cryptography API compilation errors (no API changes between these versions)

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Updated cryptography library dependency to the latest stable version

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: fea6bda8-038f-4982-b42a-b1900d523ae8

📥 Commits

Reviewing files that changed from the base of the PR and between 6ef0956 and d84ca0b.

📒 Files selected for processing (1)

• Directory.Packages.props

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📝 Walkthrough

Walkthrough

The centralized NuGet package manifest Directory.Packages.props is updated to upgrade NSec.Cryptography from pre-release version 26.1.0-preview.1 to stable release version 26.4.0. No other package versions are affected.

Changes

Dependency Version Management

Layer / File(s)	Summary
NSec.Cryptography version upgrade to 26.4.0 Directory.Packages.props	NSec.Cryptography package version is bumped from the pre-release 26.1.0-preview.1 to the stable release 26.4.0 in the centralized package manifest.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Possibly related PRs

• Harborline-Software/signal-bridge#28: Updates centralized NuGet package versions in Directory.Packages.props for a different package dependency.
• Harborline-Software/signal-bridge#8: Modifies the same Directory.Packages.props file to update centralized package version settings.
• Harborline-Software/signal-bridge#6: Changes Directory.Packages.props by bumping a different centralized NuGet package version.

Suggested labels

dependencies, .NET

Poem

A cryptographic leap, from preview to stable ground,
NSec hops forward, version twenty-six now found.
Pre-release days behind, the bridge builds strong and true,
🐰 thumps approval ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: reverting NSec.Cryptography to stable version 26.4.0, which matches the primary objective of the pull request.
Description check	✅ Passed	The description is comprehensive and well-structured, covering summary, rationale, specific changes, test plan, and references to tracking documents, though the affected projects checklist is not completed.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/nsec-revert-to-stable

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