fix(selfhost): validate Discord webhook destinations

[JSONbored]

Motivation

• Prevent posting PR disposition metadata to arbitrary endpoints by validating self-host Discord webhook URLs before use.
• Align the self-host notifier with the existing hosted notifier's allowlist to remove an SSRF/data-exfiltration vector introduced by accepting any non-empty env URL.

Description

• Add isValidDiscordWebhook with the same allowlist (discord.com, discordapp.com, canary.discord.com, ptb.discord.com) and path/scheme checks and use it in src/selfhost/discord-notify.ts to accept only https://.../api/webhooks/... URLs.
• Update resolveDiscordWebhook to return a repo-specific webhook only when it passes the new validation and to fall back to a validated global webhook otherwise, returning null when no valid Discord webhook is configured.
• Add regression tests in test/unit/selfhost-discord-notify.test.ts that cover valid Discord webhooks, repo/global fallbacks, rejection of localhost/non-Discord URLs, malformed URLs, non-Discord HTTPS hosts, and the no-op behavior when an invalid webhook is configured.

Testing

• Ran unit tests with npx vitest run test/unit/selfhost-discord-notify.test.ts, which passed (14 tests).
• Attempted type checking with npm run typecheck, which failed locally due to missing @sentry/node types in the environment.
• Attempted coverage with npm run test:coverage -- --run test/unit/selfhost-discord-notify.test.ts, which ran the tests but coverage generation failed with a remapping error (TypeError: jsTokens is not a function).
• npm audit --audit-level=moderate and npm ci failed locally due to npm registry 403 Forbidden responses, preventing a full local CI run in this environment.

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Codex Task

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.38%. Comparing base (9e1c351) to head (e49fecc).
⚠️ Report is 4 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1558   +/-   ##
=======================================
  Coverage   95.38%   95.38%           
=======================================
  Files         201      201           
  Lines       21598    21605    +7     
  Branches     7807     7808    +1     
=======================================
+ Hits        20601    20608    +7     
  Misses        416      416           
  Partials      581      581           

Files with missing lines	Coverage Δ
src/selfhost/discord-notify.ts	92.59% <100.00%> (+2.59%)	⬆️

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✅ Gittensory review — safe to merge

2 files · 1 AI reviewers · no blockers · readiness 48/100 · CI green · blocked

✅ Approved — safe to merge

Signal	Result	Evidence
Code review	✅ No blockers	1 reviewers, synthesized
Linked issue	⚠️ Missing	No linked issue or no-issue rationale found.
Related work	⚠️ 3 scoped overlaps	Top overlaps are listed below; lower-confidence bulk is hidden.
Review load	❌ 8/20	Readiness component derived from cached public PR metadata and labels; size label size:S.
Validation evidence	❌ 5/25	Cached preflight status is hold.
Open PR queue	❌ 3/10	48 open PR(s), 9 likely reviewable, 39 unlinked.
Contributor context	✅ Confirmed Gittensor contributor	JSONbored; Gittensor profile; 81 PR(s), 261 issue(s).
Gate result	✅ Passing	No configured blocker found.

Nits — 2 non-blocking

• Repository config was not parsed
• No linked issue detected — If this PR is intended to solve an issue, link it explicitly in the PR body.

Review context

• Author: JSONbored
• Role context: owner (maintainer lane)
• Public audience mode: oss maintainer
• Lane context: Repository registration is not available in the local Gittensory cache.
• Public profile languages: not available
• Official Gittensor activity: 81 PR(s), 261 issue(s).
• Related work: Titles/paths share 6 meaningful terms. (PR #1392)
• Related work: Titles/paths share 6 meaningful terms. (PR #1553)
• Related work: Titles/paths share 7 meaningful terms. (PR #1563)
• Additional title-only matches omitted; title-only overlap does not block.

Contributor next steps

• Treat this as maintainer-lane context rather than normal contributor-lane activity.
• Explain no-issue PR.
• Review top overlaps.
• Add scope summary.
• Fix blocker.
• Expect slower review.
• Refresh registry data or choose a registered active repo.
• Link the issue being solved, or explicitly explain why this is a no-issue PR.
• Check active issues and PRs before submitting.

Signal definitions

• Related work = same linked issue, overlapping active PRs, or title/path similarity.
• Review load = cached public PR metadata such as size labels, changed paths, and preflight status.
• Open PR queue = repo-wide review pressure; it is not a PR quality failure.
• Contributor context = public GitHub/Gittensor identity context; non-Gittensor status is not a blocker.

_{🟩 Safe / merged · 🟦 Advisory · 🟨 Held for review · 🟥 Blocked / closed}

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