*: fix exit sig agg

[KaloyanTanev]

Lagrange interpolation of non-contiguous shares was failing before...

With this change though, we do require beacon node endpoints to be set when calling the fetch exit, so that we can verify the signatures (we need the Domain from the BN's spec). We can think of storing mainnet, hoodi and sepolia specs in the charon repo, so we can reference them locally and skip this one.

category: bug
ticket: none

[Copilot]

Pull request overview

This PR fixes full-exit signature aggregation when returned partial signatures do not map directly to contiguous share positions by resolving share indices via BLS verification against validator public shares.

Changes:

• Requires beacon node configuration for exit fetch so exit signing domains can be derived.
• Passes validator public shares and an eth2 client through fetch/broadcast full-exit paths.
• Updates obolapi.GetFullExit to verify partial signatures, recover share indices, aggregate, and validate the final signature; adds non-contiguous-share test coverage.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
cmd/exit_fetch.go	Adds beacon-node flags/client creation and passes pub shares into full-exit retrieval.
cmd/exit_fetch_internal_test.go	Updates fetch tests/CLI args for required beacon-node endpoint configuration.
cmd/exit_broadcast.go	Threads eth2 client into Obol API full-exit retrieval and resolves pub shares from the lock.
cmd/exit_broadcast_internal_test.go	Updates broadcast tests for the new exitFromObolAPI signature.
app/obolapi/exit.go	Reworks full-exit aggregation to identify partial signature share indices via BLS verification.
app/obolapi/exit_test.go	Updates existing tests and adds coverage for non-contiguous share aggregation.

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[codecov]

Codecov Report

❌ Patch coverage is 64.28571% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.08%. Comparing base (2c42245) to head (0fff454).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
app/obolapi/exit.go	51.42%	9 Missing and 8 partials ⚠️
cmd/exit_fetch.go	68.42%	3 Missing and 3 partials ⚠️
cmd/exit_broadcast.go	87.50%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4542      +/-   ##
==========================================
+ Coverage   57.01%   57.08%   +0.06%     
==========================================
  Files         245      245              
  Lines       32971    33055      +84     
==========================================
+ Hits        18799    18868      +69     
- Misses      11789    11797       +8     
- Partials     2383     2390       +7     

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud