feat(errors): add SignatureVerificationError

[Tijesunimi004]

Summary

Adds SignatureVerificationError(ShadeError) to errors.py, closes #34.

• Stores the raw Shade-Signature header value as received (header attribute).
• SignatureVerificationError.from_mismatch(header=...) factory builds the error with a message explaining the likely causes (wrong webhook secret or payload modified in transit), mirroring the existing NotFoundError.from_response / InvalidRequestError.from_response pattern.
• The expected signature is never accepted as an argument anywhere on this class, so it cannot end up in the exception message or attributes.
• Exported from the shade package root.

This only adds the error type per the issue's proposed steps. Webhook.construct_event() (issue #66) will raise it once implemented.

Test plan

• pytest tests/test_errors.py — new tests cover: inherits from ShadeError, header is optional, from_mismatch stores the header, the message mentions both "secret" and "payload", and the expected signature never appears in the message or as an attribute.
• Full suite (pytest) passes: 137 passed.
• flake8 . --count --select=E9,F63,F7,F82 (CI's hard-fail lint check) passes clean.

Summary by CodeRabbit

• New Features

  • Added a public SignatureVerificationError exception for webhook signature/HMAC verification failures.
  • Error details can optionally include the received signature header and standardized guidance for signature mismatches.
  • The exception is now available directly from the shade package.

• Tests

  • Added coverage for subclassing from ShadeError, optional header behavior, mismatch message construction, and ensuring no expected-signature values are exposed.

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[coderabbitai]

📝 Walkthrough

Walkthrough

A new SignatureVerificationError represents webhook signature mismatches, stores an optional raw signature header, exposes a mismatch factory, and is publicly exported from shade. Tests cover inheritance, messaging, header handling, and signature secrecy.

Changes

Signature verification error

Layer / File(s)	Summary
Signature verification exception src/shade/errors.py	Defines SignatureVerificationError with optional header storage and a standardized mismatch message factory.
Public export and behavior validation src/shade/__init__.py, tests/test_errors.py	Exports the exception at the package root and tests inheritance, header handling, message contents, and protection of expected signatures.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related issues

• Implement SignatureVerificationError #34 — Directly describes implementing SignatureVerificationError, including header storage, mismatch messaging, and expected-signature protection.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title is concise and accurately summarizes the main change: adding SignatureVerificationError.
Description check	✅ Passed	The description covers the summary, issue link, motivation/context, and test plan; only non-critical template sections are missing.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[codebestia]

Hello @Tijesunimi004
Please properly link the issue using the Closes keyword and fix the merge conflicts.
Thanks.

[Tijesunimi004]

All fixed and done @codebestia

[codebestia]

LGTM!
Thank you for your contribution.