Replace usage of Fatale with context cancellation

[ggilder]

Related issue: #1635

Description

This PR replaces log.Fatale error handling in listenOnPanicAbort() with context-based cancellation and proper error propagation, enabling gh-ost to be used as a Go library while maintaining the same CLI behavior.

The previous implementation called Fatale in a separate goroutine when fatal errors occurred. This had several issues:

• Could not be recovered by the caller
• Library users had no way to handle errors gracefully
• Process would crash instead of returning errors
• Violates Go best practices ("libraries should return errors, not panic")

I've implemented a context-based cancellation system with proper error propagation:

1. Error Storage: Added AbortError field to MigrationContext with thread-safe accessor methods that implement "first error wins" semantics
2. Context Cancellation: Added context.Context to MigrationContext for coordinated shutdown signaling across all goroutines
3. Graceful Shutdown: Updated listenOnPanicAbort() to store errors and cancel context instead of exiting the process
4. Abort Checks: Added checkAbort() helper that checks for stored errors at key points in Migrate() and Revert()
5. Goroutine Integration: Updated all long-running goroutines (heartbeat, streaming, throttling, row iteration) to respect context cancellation

This also makes abort scenarios more testable.

• contributed code is using same conventions as original code
• script/cibuild returns with no formatting errors, build errors or unit test errors.

[Copilot]

Pull request overview

This PR replaces abort handling that previously exited the process (log.Fatale) with context cancellation + “first error wins” error propagation, improving gh-ost’s usability as a library while preserving CLI behavior.

Changes:

• Added context.Context + abort error storage to MigrationContext, and cancelled context on abort.
• Updated long-running loops and abort send sites to respect context cancellation.
• Added unit tests for abort propagation and first-error-wins behavior.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
go/base/context.go	Adds cancellable context + abort error storage APIs to MigrationContext.
go/base/context_test.go	Tests for first-error-wins abort error storage and thread-safety.
go/logic/migrator.go	Replaces Fatale with error storage + context cancellation; adds checkAbort() and integrates it into migration flow.
go/logic/migrator_test.go	New tests validating abort propagation and checkAbort() behavior.
go/logic/applier.go	Heartbeat loop now exits on context cancellation; abort send is context-aware.
go/logic/throttler.go	Throttle checks now exit on context cancellation; abort sends are context-aware.
go/logic/streamer.go	Streaming loop now checks for context cancellation.
go/logic/server.go	“panic” command abort send is context-aware.

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[meiji163]

This is great!

[meiji163]

@GGlider Looks like the migration tests are hanging for some reason. I'll take a look later if I get the chance

[ggilder]

@meiji163 hmm, interesting. I did see some tests hanging locally before, and I thought I had resolved that. However I just tried running locally and it's hanging at the same spot. I'll take another look on Monday.

[ggilder]

@meiji163 think I found the spot that was deadlocking, and I added a helper to encapsulate the non-blocking channel send pattern. I believe the replica tests should pass now

[ggilder]

Looks like it's still hanging somewhere 😢 I'll keep testing, maybe I can run the tests in a container to more closely approximate CI.

[ggilder]

@meiji163 could you approve the workflow run again? I think this latest commit will fix it