feat(output): change resubscription method

[Molter73]

Description

The new way for output components to resubscribe the broadcast channel distributing events is to send a oneshot sender back to the main task which will resubscribe from the broadcast sender and forward the receiver back.

While this approach might seem overly complicated, it ensures there will be no lingering receivers laying around, which in turn allows for Arc::unwrap_or_clone to properly unwrap all messages when only one output is in use.

Checklist

• Patch has a change log entry OR does not need one.
• Investigated and inspected CI test results
• Updated documentation accordingly

Automated testing

• Added unit tests
• Added integration tests
• Added regression tests

If any of these don't apply, please comment below.

Testing Performed

Used the changes from #1010 to run fact under DHAT with and without these changes. Without these changes the call to Arc::unwrap_or_clone in fact/src/output/grpc.rs is showing up as making a clone, with the changes this doesn't happen anymore.

[coderabbitai]

📝 Walkthrough

Walkthrough

The gRPC output client now requests a fresh broadcast receiver per connection through an mpsc/oneshot handshake. The output module adds an EventReceiver alias and subscription servicing, and the stdout client switches to the new receiver type.

Changes

Subscriber-based event receiver plumbing

Layer / File(s)	Summary
EventReceiver alias and subscription channel wiring fact/src/output/mod.rs	Adds EventReceiver type alias, creates an mpsc subscription channel passed into grpc::Client::new, starts stdout directly with broad_rx, extends the select loop to service subscription requests by subscribing per-request, and revises task termination/error handling (Ok(()) vs bail!).
gRPC Client subscriber field and stream setup fact/src/output/grpc.rs	Replaces stored broadcast::Receiver with subscriber: mpsc::Sender<oneshot::Sender<EventReceiver>> in Client/Client::new, and updates run() to request an EventReceiver via oneshot before wrapping it in BroadcastStream, preserving lag/metrics handling.
stdout Client type update fact/src/output/stdout.rs	Updates Client's rx field and Client::new parameter from broadcast::Receiver<Arc<Event>> to EventReceiver, removing now-unused imports.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Suggested reviewers: JoukoVirtanen, Stringy

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title is concise and accurately describes the main change to output resubscription behavior.
Description check	✅ Passed	The description follows the template with a clear summary, checklist, and testing notes, with only documentation left unchecked.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch mauro/feat/resubscription-change

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.64%. Comparing base (baebc56) to head (c98bda1).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
fact/src/output/grpc.rs	0.00%	15 Missing ⚠️
fact/src/output/mod.rs	0.00%	14 Missing ⚠️
fact/src/output/stdout.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1011      +/-   ##
==========================================
- Coverage   33.85%   32.64%   -1.21%     
==========================================
  Files          21       21              
  Lines        2812     2916     +104     
  Branches     2812     2916     +104     
==========================================
  Hits          952      952              
- Misses       1857     1961     +104     
  Partials        3        3              

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@fact/src/output/mod.rs`:
- Around line 60-65: The `tokio::select!` branch in `output::mod::start` that
reads from `subs_rx.recv()` should treat a closed subscription channel as
terminal instead of continuing. Update the `req = subs_rx.recv()` handling so
`None` breaks the loop or returns an error/finished state, and keep the existing
`req.send(rx)` path for valid requests. This prevents the `subs_rx` branch from
becoming immediately ready forever and lets the output task shut down cleanly.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Enterprise

Run ID: 3b392f6c-31a6-4820-9a4e-d01a8281fa7f

📥 Commits

Reviewing files that changed from the base of the PR and between 17d94b4 and c51ec30.

📒 Files selected for processing (3)

• fact/src/output/grpc.rs
• fact/src/output/mod.rs
• fact/src/output/stdout.rs