feat(alerts): add webhook2 channel with custom headers and timeout

[marvelousjeremiah24]

Adds a new built-in alert channel 'webhook2' that accepts a JSON-encoded target string {url, headers?, timeoutMs?}, enabling per-config custom HTTP headers and timeout overrides without touching the existing webhook channel.

• src/alerts/webhook2.ts: new channel implementation with parseWebhook2Target() for robust validation, custom header merging, configurable timeout (default 10 000 ms), and identical HMAC-SHA256 signing to the original webhook channel
• src/alerts/builtins.ts: additive-only change — registers 'webhook2' alongside the existing five channels; original webhook registration is untouched
• tests/alerts/webhook2.test.ts: 32 TDD tests covering target parsing, HTTP request shape, custom headers, HMAC signing, timeout override, success/error handling, and registry integration
• tests/alerts/builtins.test.ts: updated channel-count and signing assertions to reflect the new six-channel registry; added webhook2 delegation and missingTargetError tests

What does this PR do?

Why?

Does this touch secret-key handling or transaction submission?

• Yes — see notes above
• No

Checklist

• Tests pass (npm test)
• Type check passes (npx tsc --noEmit)
• Lint passes (npm run lint)
• Tests cover the new functionality (TDD preferred — see CONTRIBUTING.md)
• No unnecessary dependencies added
• Commit messages follow conventional format
• No console.log in core logic
• ADR added if this is a significant design decision (see docs/adr)
• E2E sandbox tested, if this touches RPC or daemon behavior (see docs/e2e-sandbox.md)
• closes feat(alerts): add generic Webhook v2 channel with configurable retry policy #327

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📥 Commits

Reviewing files that changed from the base of the PR and between 35d9237 and 25a6e6d.

📒 Files selected for processing (4)

• src/alerts/builtins.ts
• src/alerts/webhook2.ts
• tests/alerts/builtins.test.ts
• tests/alerts/webhook2.test.ts

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[gitguardian]

⚠️ GitGuardian has uncovered 1 secret following the scan of your pull request.

Please consider investigating the findings and remediating the incidents. Failure to do so may lead to compromising the associated services or software components.

Since your pull request originates from a forked repository, GitGuardian is not able to associate the secrets uncovered with secret incidents on your GitGuardian dashboard.
Skipping this check run and merging your pull request will create secret incidents on your GitGuardian dashboard.

🔎 Detected hardcoded secret in your pull request

GitGuardian id	GitGuardian status	Secret	Commit	Filename
-	-	Generic High Entropy Secret	ded54f4	tests/commands/guard-cli-export-import.test.ts	View secret

🛠 Guidelines to remediate hardcoded secrets

1. Understand the implications of revoking this secret by investigating where it is used in your code.
2. Replace and store your secret safely. Learn here the best practices.
3. Revoke and rotate this secret.
4. If possible, rewrite git history. Rewriting git history is not a trivial act. You might completely break other contributing developers' workflow and you risk accidentally deleting legitimate data.

To avoid such incidents in the future consider

• following these best practices for managing and storing secrets including API keys and other credentials
• install secret detection on pre-commit to catch secret before it leaves your machine and ease remediation.

---

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[AbdulmalikAlayande]

Merged into main (dbdd9cc) after local verification (tsc, lint, full suite 1244/1244, npm audit, build) and a manual smoke test confirming alerts channels lists both webhook and webhook2 correctly. Clean implementation — the JSON-blob-in-target design to avoid a schema change is a sensible tradeoff, and the original webhook channel's tests all still pass untouched. Only had to resolve a small merge conflict in the channel-count assertions (10→11 channels now that other channels landed in the meantime). Thanks!