[malo-denielou]

When runners require deterministic pipeline graphs across restarts (such as for pipeline graph equality checks on controller failover), two map-iteration paths in the Go SDK can produce non-deterministic ordering:

1. In pipelinex.computeRoots, root transform IDs are collected by ranging over xforms (map[string]*pipepb.PTransform) and passed directly to TopologicalSort(xforms, roots). While TopologicalSort already sorts its internal frontier (ret.next) and output keys for determinism, the initial roots slice was left in random map iteration order. Sorting roots with sort.Sort(idSorted(roots)) makes the root topological order deterministic.
2. In xlangx.HandlerParams.Inputs() and Outputs(), PCol entries are collected by ranging over InputsMap and OutputsMap (map[string]int) in random order, which can cause expansion handlers to register cross-language inputs or outputs in varying orders across runs. Sorting the returned slice by PCol.Index (with PCol.Local as a tie-breaker) ensures a consistent order while still supporting sparse index maps (such as when xlang.SetOutputCoder rewrites OutputsMap to a single entry at an index greater than 0).

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[github-actions]

📋 Review Summary

This PR resolves non-deterministic ordering in pipelinex.computeRoots and xlangx.HandlerParams (Inputs() and Outputs()) caused by Go map iteration order. The changes are minimal, idiomatic, and well-tested.

🔍 General Feedback

• Sorting roots with idSorted prior to TopologicalSort in computeRoots aligns with how transform IDs are ordered elsewhere in pipelinex.
• Sorting PCol slices by Index (with Local as a tie-breaker) in HandlerParams.Inputs() and Outputs() cleanly guarantees deterministic ordering while preserving support for sparse index maps.
• The added unit tests thoroughly cover both determinism across iterations and sparse index edge cases.

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Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 28.97%. Comparing base (0f1ac43) to head (e06cc8c).
⚠️ Report is 16 commits behind head on master.

Files with missing lines	Patch %	Lines
sdks/go/pkg/beam/core/runtime/xlangx/registry.go	83.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #40880       +/-   ##
===========================================
+ Coverage        0   28.97%   +28.97%     
===========================================
  Files           0      382      +382     
  Lines           0    71223    +71223     
===========================================
+ Hits            0    20635    +20635     
- Misses          0    48733    +48733     
- Partials        0     1855     +1855     

Flag	Coverage Δ
go	28.97% <85.71%> (?)

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[github-actions]

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[shunping]

LGTM, thanks!