refactor(pipeline): deduplicate scheduler constants and shared functions

[nh13]

Summary

• Replace per-scheduler STEPS constant (11 copies) with existing PipelineStep::all() method
• Replace per-scheduler step_index() method (10 copies) with existing PipelineStep::index() method
• Extract shared balanced_chase_determine_role() to scheduler/mod.rs, replacing identical copies in balanced_chase.rs and balanced_chase_drain.rs

Net: -204 lines across 12 files.

Test plan

• cargo nextest run -p fgumi --filter-expr 'test(scheduler) | test(pipeline) | test(unified)' — 339 tests pass
• cargo ci-fmt — clean
• cargo ci-lint — clean

[codecov]

Codecov Report

❌ Patch coverage is 82.66667% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.86%. Comparing base (3a460ea) to head (5a7c603).
⚠️ Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/lib/unified_pipeline/scheduler/balanced_chase.rs	66.66%	3 Missing ⚠️
...lib/unified_pipeline/scheduler/chase_bottleneck.rs	84.61%	2 Missing ⚠️
...c/lib/unified_pipeline/scheduler/epsilon_greedy.rs	50.00%	2 Missing ⚠️
...lib/unified_pipeline/scheduler/learned_affinity.rs	50.00%	2 Missing ⚠️
...unified_pipeline/scheduler/thompson_with_priors.rs	33.33%	2 Missing ⚠️
.../lib/unified_pipeline/scheduler/optimized_chase.rs	87.50%	1 Missing ⚠️
...unified_pipeline/scheduler/sticky_work_stealing.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #150      +/-   ##
==========================================
+ Coverage   83.61%   83.86%   +0.25%     
==========================================
  Files         126      127       +1     
  Lines       51510    51148     -362     
==========================================
- Hits        43069    42895     -174     
+ Misses       8441     8253     -188     

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Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: f6853a94-cf95-44e4-84f1-71b664867358

📥 Commits

Reviewing files that changed from the base of the PR and between 51b236c and 5a7c603.

📒 Files selected for processing (12)

• src/lib/unified_pipeline/scheduler/backpressure_proportional.rs
• src/lib/unified_pipeline/scheduler/balanced_chase.rs
• src/lib/unified_pipeline/scheduler/balanced_chase_drain.rs
• src/lib/unified_pipeline/scheduler/chase_bottleneck.rs
• src/lib/unified_pipeline/scheduler/epsilon_greedy.rs
• src/lib/unified_pipeline/scheduler/learned_affinity.rs
• src/lib/unified_pipeline/scheduler/mod.rs
• src/lib/unified_pipeline/scheduler/optimized_chase.rs
• src/lib/unified_pipeline/scheduler/sticky_work_stealing.rs
• src/lib/unified_pipeline/scheduler/thompson_sampling.rs
• src/lib/unified_pipeline/scheduler/thompson_with_priors.rs
• src/lib/unified_pipeline/scheduler/ucb.rs

📝 Walkthrough

Walkthrough

This pull request refactors scheduler implementations to use dynamic step resolution instead of static constants. Static STEPS arrays and helper methods like step_index() are removed across multiple scheduler files and replaced with PipelineStep::all() for runtime retrieval. Direct index access via step.index() replaces the previous lookup approach. A new non-public helper function balanced_chase_determine_role() is added to the scheduler module. Public API signatures remain unchanged; changes are internal implementation refactors affecting approximately 13 files with net reduction in lines of code.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	Title clearly and concisely summarizes the main refactoring goal: deduplicating scheduler constants and functions across the codebase.
Description check	✅ Passed	Description accurately details the three main changes (STEPS deduplication, step_index replacement, shared function extraction) with test results and net line reduction.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch refactor/nh/simplify-fgumi-pipeline

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Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

src/lib/unified_pipeline/scheduler/balanced_chase.rs (1)

39-58: ⚠️ Potential issue | 🟠 Major

Add num_threads > 0 guard to constructor before delegating to helper.

The helper balanced_chase_determine_role() evaluates num_threads - 1 and num_threads - 2 in conditions (lines 369, 373 in mod.rs). These expressions are evaluated before their corresponding guards (num_threads > 1, num_threads > 3), causing panics in debug builds if num_threads == 0. Adding a precondition in the constructor prevents this class of error at the call boundary.

Proposed fix

 pub fn new(thread_id: usize, num_threads: usize, active_steps: ActiveSteps) -> Self {
+    assert!(num_threads > 0, "num_threads must be > 0");
     let (current_step, exclusive_role) = Self::determine_role(thread_id, num_threads);

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/lib/unified_pipeline/scheduler/balanced_chase.rs` around lines 39 - 58,
In the constructor new(thread_id, num_threads, active_steps) add a precondition
that num_threads > 0 before calling determine_role to avoid downstream underflow
in balanced_chase_determine_role; e.g., validate (panic/assert) with a clear
message or return an error when num_threads == 0, then call
Self::determine_role(thread_id, num_threads) as before so determine_role and
balanced_chase_determine_role never see num_threads == 0.

🧹 Nitpick comments (1)

src/lib/unified_pipeline/scheduler/backpressure_proportional.rs (1)

85-87: Hoist PipelineStep::all() outside the loop.

Small readability/perf improvement: avoid rebuilding the step array each iteration.

♻️ Proposed refactor

-        for (priority, (_, step_idx)) in weighted.iter().enumerate() {
-            self.priority_buffer[priority] = PipelineStep::all()[*step_idx];
-        }
+        let steps = PipelineStep::all();
+        for (priority, (_, step_idx)) in weighted.iter().enumerate() {
+            self.priority_buffer[priority] = steps[*step_idx];
+        }

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/lib/unified_pipeline/scheduler/backpressure_proportional.rs` around lines
85 - 87, The loop repeatedly calls PipelineStep::all(), rebuilding the same
array each iteration; hoist that call out of the for-loop by assigning let
all_steps = PipelineStep::all() before iterating and then use
all_steps[*step_idx] when populating self.priority_buffer[priority] (the loop
over weighted, the priority_buffer assignment and the weighted/step_idx
variables identify the spot to change).

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Outside diff comments:
In `@src/lib/unified_pipeline/scheduler/balanced_chase.rs`:
- Around line 39-58: In the constructor new(thread_id, num_threads,
active_steps) add a precondition that num_threads > 0 before calling
determine_role to avoid downstream underflow in balanced_chase_determine_role;
e.g., validate (panic/assert) with a clear message or return an error when
num_threads == 0, then call Self::determine_role(thread_id, num_threads) as
before so determine_role and balanced_chase_determine_role never see num_threads
== 0.

---

Nitpick comments:
In `@src/lib/unified_pipeline/scheduler/backpressure_proportional.rs`:
- Around line 85-87: The loop repeatedly calls PipelineStep::all(), rebuilding
the same array each iteration; hoist that call out of the for-loop by assigning
let all_steps = PipelineStep::all() before iterating and then use
all_steps[*step_idx] when populating self.priority_buffer[priority] (the loop
over weighted, the priority_buffer assignment and the weighted/step_idx
variables identify the spot to change).

---

ℹ️ Review info

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 3a460ea and 51b236c.

📒 Files selected for processing (12)

• src/lib/unified_pipeline/scheduler/backpressure_proportional.rs
• src/lib/unified_pipeline/scheduler/balanced_chase.rs
• src/lib/unified_pipeline/scheduler/balanced_chase_drain.rs
• src/lib/unified_pipeline/scheduler/chase_bottleneck.rs
• src/lib/unified_pipeline/scheduler/epsilon_greedy.rs
• src/lib/unified_pipeline/scheduler/learned_affinity.rs
• src/lib/unified_pipeline/scheduler/mod.rs
• src/lib/unified_pipeline/scheduler/optimized_chase.rs
• src/lib/unified_pipeline/scheduler/sticky_work_stealing.rs
• src/lib/unified_pipeline/scheduler/thompson_sampling.rs
• src/lib/unified_pipeline/scheduler/thompson_with_priors.rs
• src/lib/unified_pipeline/scheduler/ucb.rs