feat(go): add stream/topic purge API with BDD tests and fix server purge bug

[chengxilo]

Which issue does this PR address?

Relates to #2148

Rationale

Go SDK doesn't have the purge topic/ purge stream API, so this PR implement them. To test it, I added an new BDD test scenario, and implemented both Go and Rust BDD tests.

What changed?

The Go SDK was missing PurgeStream and PurgeTopic methods. Added them along with a shared BDD scenario (stream_topic_purge.feature) and implementations in both Go and Rust.

While testing, discovered that purge_all_segments only cleared on-disk segments but left stale messages in the journal and in-flight tiers. Polling after purge would return messages that should have been deleted. Fixed by calling journal.reset() and clear_in_flight() during partition re-initialization. I am not famliar with Rust server code so during the code review this part worth more attention

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

1. DeepSeek pro v4, Claude Opus 4.6
2. DeepSeek pro v4 for BDD test implementation, Claude Opus 4.6 for server bug fixing.
3. I reviewed them with my best effert, the bdd scripts are executed and actually works, and they found that there is a bug in the server so I believe they works.
4. I hope so.

[github-actions]

Thanks for the PR. It is labeled S-waiting-on-review and queued for review.

Slash commands (own line, regular comment) move it around the queue:

• /ready - back to S-waiting-on-review after addressing feedback
• /author - flip to S-waiting-on-author while you finish changes
• /request-review @user-or-team - request a reviewer

See CONTRIBUTING.md for details.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.68%. Comparing base (fb9307e) to head (2943e47).

Files with missing lines	Patch %	Lines
foreign/go/internal/command/stream.go	0.00%	4 Missing ⚠️
foreign/go/internal/command/topic.go	0.00%	4 Missing ⚠️
foreign/go/client/tcp/tcp_stream_management.go	0.00%	3 Missing ⚠️
foreign/go/client/tcp/tcp_topic_management.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3608      +/-   ##
============================================
- Coverage     82.84%   82.68%   -0.17%     
+ Complexity     1299     1291       -8     
============================================
  Files          1199     1199              
  Lines        161885   160224    -1661     
  Branches     131360   129822    -1538     
============================================
- Hits         134120   132475    -1645     
- Misses        24225    24234       +9     
+ Partials       3540     3515      -25     

Components	Coverage Δ
Rust Core	83.18% <ø> (-0.18%)	⬇️
Java SDK	66.12% <ø> (+0.05%)	⬆️
C# SDK	75.65% <ø> (-0.32%)	⬇️
Python SDK	89.98% <ø> (ø)
PHP SDK	84.26% <ø> (ø)
Node SDK	96.24% <ø> (+0.03%)	⬆️
Go SDK	68.42% <0.00%> (-0.12%)	⬇️

Files with missing lines	Coverage Δ
foreign/go/client/tcp/tcp_stream_management.go	78.04% <0.00%> (-6.17%)	⬇️
foreign/go/client/tcp/tcp_topic_management.go	88.13% <0.00%> (-4.73%)	⬇️
foreign/go/internal/command/stream.go	83.78% <0.00%> (-10.16%)	⬇️
foreign/go/internal/command/topic.go	87.17% <0.00%> (-4.72%)	⬇️

... and 46 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[hubcio]

@chengxilo i'll check this during the weekend. could you please rebase?

[numinnex]

I've checked whether there is potential concurrency issue due to interleaving of flush + purge commands as this is what I've reckon from the changes could potentially be an issue and did not find any problems with that. Let's wait for @hubcio review and we can merge it.

[chengxilo]

/ready

[chengxilo]

nothing has been changed, just because I rebased onto master locally so it was forced pushed() I shouldn't do that tho.

[hubcio]

@chengxilo could you please rebase again? i will review this today

[chengxilo]

@chengxilo could you please rebase again? i will review this today

done. Currently, we get the pre-purge messages back for roughly > a second. I'm not sure if we should justify it in BDD test or fix it. Previously for the non-VSR it was fixed. But not for the VSR enabled one. (since according to the comments, it was intended)