Harden X publishing retries and sample concurrency

[cdcavell]

Summary

• stop retrying ambiguous X POST failures after network errors or HTTP 5xx responses while retaining safe 429 retries
• use UTF-8 OAuth signing, inject the OAuth timestamp for tests, and avoid tight Retry-After loops
• synchronize the bounded-use sample read, document process-lifetime state retention, and expand .NET artifact ignores

Validation

• dotnet run --file tools/publish-x.cs -- --self-test
• dotnet restore samples/Samples.slnx --locked-mode
• dotnet build samples/Samples.slnx --configuration Release --no-restore
• dotnet format samples/Samples.slnx --verify-no-changes --no-restore --verbosity minimal
• dotnet test samples/Samples.slnx --configuration Release --no-build (300 passed)

[Copilot]

Copilot review overview

🟡 Changes recommended

The OAuth self-test does not validate the generated signature, leaving signing regressions undetected.

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Review effort: Lite
Findings: 1

Open (1)

• OAuth test fails to validate generated signature · New

What changed in this PR

Hardens X publishing retries and improves concurrency handling and documentation in the bounded-use sample.

Changes:

• Avoids unsafe POST retries while retaining bounded 429 retries.
• Adds UTF-8 OAuth signing and injectable timestamps.
• Synchronizes sample use-count reads and expands .NET artifact ignores.

File	Summary
tools/​publish-x.cs	Retry, OAuth, and self-test updates. Moderate finding: the self-test should assert the OAuth signature using deterministic inputs.
samples/​replay-protection-and-bounded-use/​Sample/​ReplayProtection.cs	Thread-safe use-count observation and lifecycle documentation.
.gitignore	Additional IDE, test, coverage, and package artifact ignores.

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[Copilot]

Copilot review overview

🔵 Needs a closer look

Retry semantics, OAuth signing, and concurrency changes warrant final human review.

Review effort: Lite
Findings: None

Resolved since last review (1)

• OAuth test fails to validate generated signature