fix(beacon): centralize LOTUS_IGNORE_DRAND guard across all drand code paths

[exp0nge]

Summary

• Extends the existing LOTUS_IGNORE_DRAND env var guard so it covers every path to a DrandBeacon, not only RandomSchedule. Previously, any DrandBeacon that leaked past the RandomSchedule early-return could still reach external drand servers — the env var semantics were inconsistent.
• Adds defense-in-depth guards in DrandBeacon.Entry (returns a deterministic 96-byte zero stub) and DrandBeacon.VerifyEntry (returns nil) in chain/beacon/drand/drand.go, so any DrandBeacon that bypasses the RandomSchedule guard no-ops at request time.
• Keeps the original RandomSchedule early-return in node/modules/services.go as the primary guard; the per-method guards are a safety net for hermetic / network-isolated test environments.

Test plan

• TestIgnoreDrandEntry — verifies DrandBeacon.Entry returns a 96-byte zero stub with the correct round when LOTUS_IGNORE_DRAND is set
• TestIgnoreDrandVerifyEntry — verifies DrandBeacon.VerifyEntry returns nil (no error) when LOTUS_IGNORE_DRAND is set
• Existing TestMaxBeaconRoundForEpoch and TestQuicknetIsChained still pass (no regressions)
• CI is green

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR aims to make LOTUS_IGNORE_DRAND consistently prevent any drand network access by guarding all drand-beacon code paths (not just RandomSchedule), with added defense-in-depth no-op behavior at request/verification time.

Changes:

• Add an early-return mock beacon schedule when LOTUS_IGNORE_DRAND is set.
• Add per-method short-circuits in DrandBeacon.Entry and DrandBeacon.VerifyEntry when LOTUS_IGNORE_DRAND is set.
• Add tests covering the ignore behavior for Entry and VerifyEntry, plus a changelog entry.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

File	Description
node/modules/services.go	Adds LOTUS_IGNORE_DRAND guard to return a mock beacon schedule early.
chain/beacon/drand/drand.go	Adds defense-in-depth guards to stub Entry and skip VerifyEntry under LOTUS_IGNORE_DRAND.
chain/beacon/drand/drand_test.go	Adds tests validating the ignore behavior for entry retrieval and verification.
CHANGELOG.md	Documents the behavioral change in the unreleased changelog.

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[Copilot]

Pull request overview

Extends the LOTUS_IGNORE_DRAND behavior so all drand-backed randomness paths reliably short-circuit in hermetic / network-isolated environments, preventing any accidental dialing of external drand endpoints.

Changes:

• Add an early-return in RandomSchedule to use a mock beacon schedule when LOTUS_IGNORE_DRAND=_yes_.
• Add defense-in-depth guards in DrandBeacon.Entry and DrandBeacon.VerifyEntry to no-op when LOTUS_IGNORE_DRAND=_yes_.
• Add unit tests covering the new DrandBeacon ignore behavior and document the change in the changelog.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
node/modules/services.go	Returns a mock beacon schedule when LOTUS_IGNORE_DRAND is enabled to avoid any drand network usage.
chain/beacon/drand/drand.go	Adds per-method LOTUS_IGNORE_DRAND short-circuiting in Entry and VerifyEntry.
chain/beacon/drand/drand_test.go	Adds tests validating the new ignore behavior for Entry and VerifyEntry.
CHANGELOG.md	Notes the behavioral change under UNRELEASED bug fixes.

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