BE-524: HashQL: Remove island schedule module

[indietyp]

🌟 What is the purpose of this PR?

The island::schedule module, which provided topological scheduling with parallelism level assignment for execution islands, has been removed. This includes the IslandSchedule and ScheduledIsland types, the schedule and schedule_in methods on IslandGraph, and all associated tests. The scheduling functionality is no longer needed or has been superseded by an alternative approach.

🔍 What does this change?

• Removes the schedule submodule from island/mod.rs
• Deletes island/schedule/mod.rs, which contained the IslandSchedule and ScheduledIsland types along with the Kahn's algorithm-based topological level assignment implementation
• Deletes island/schedule/tests.rs, which contained tests for level ordering, contiguity, and full node coverage of the schedule
• Removes the public re-exports of IslandSchedule and ScheduledIsland from pass/execution/mod.rs

Pre-Merge Checklist 🚀

🚢 Has this modified a publishable library?

This PR:

• does not modify any publishable blocks or libraries, or modifications do not need publishing

📜 Does this require a change to the docs?

The changes in this PR:

• are internal and do not require a docs change

🕸️ Does this require a change to the Turbo Graph?

The changes in this PR:

• do not affect the execution graph

🛡 What tests cover this?

The tests that previously covered the scheduling logic have been removed alongside the implementation.

❓ How to test this?

1. Checkout the branch
2. Run cargo test in libs/@local/hashql/mir
3. Confirm that the build succeeds and no references to IslandSchedule or ScheduledIsland remain

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[cursor]

PR Summary

Low Risk
Dead-code removal with no remaining references; execution analysis still builds IslandGraph the same way.

Overview
Removes the island scheduling layer from HashQL MIR execution: the island::schedule submodule and its public exports (IslandSchedule, ScheduledIsland) are deleted entirely.

That module implemented Kahn-style topological ordering of IslandGraph nodes with parallelism levels (same-level islands were treated as independent). IslandGraph::schedule / schedule_in and the dedicated schedule tests go with it. Island placement and IslandGraph construction in ExecutionAnalysis are unchanged; only the optional schedule-on-graph API is gone.

^{Reviewed by Cursor Bugbot for commit 5aa1fb4. Bugbot is set up for automated code reviews on this repo. Configure here.}

[indietyp]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• BE-513: HashQL: Rework dynamic aggregate size estimation #8697
• BE-512: HashQL: Allow cross-backend transitions for SwitchInt terminators #8696
• BE-524: HashQL: Remove island schedule module #8694 👈 (View in Graphite)
• BE-525: HashQL: Remove implicit type-widening from Integer operations, and make comparison size aware #8693
• BE-515: HashQL: Remove OFFSET 0 materialization fence from generated query #8650
• BE-514: HashQL: implement iterative adjustment passes in placement solver #8635
• BE-500, BE-501: HashQL: Unify mixed parameter resolution in data dependency analysis #8607
• BE-494: HashQL: Loop-breaker selection for recursive inlining #8600
• BE-482: HashQL: Remove logical not from MIR and fix postgres boolean lowering #8595
• BE-474: HashQL: Take into account terminator target eligibility in execution backend placement #8587
• BE-455: HashQL: Introduce evaluation orchestrator #8586
• BE-523: HashQL: Suspendable interpreter with structured values and input system #8675
• BE-522: HashQL: Expand stdlib type system with temporal types #8674
• BE-306: HashQL: PostgreSQL translation #8526
• BE-457: HashQL: MIR execution pipeline extensions for postgres compilation #8525
• BE-456: HashQL: Entity type model enrichment and graph store query extensions #8524
• BE-429: HashQL: Add island dependency graph with data requirement resolution #8501
• BE-428: HashQL: Simplify traversal tracking to path recording #8498
• BE-434: HashQL: Refactor entity storage path resolution with centralized schema mapping #8496
• BE-427: Add hashql-macros crate with procedural macros for ID types and symbols #8495
• main

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[augmentcode]

🤖 Augment PR Summary

Summary: Removes the deprecated/unused HashQL MIR island scheduling implementation and its public surface area.

Changes:

• Drops the pass::execution::island::schedule submodule from island/mod.rs
• Deletes the scheduling implementation (IslandGraph::schedule/schedule_in) and the related types (IslandSchedule, ScheduledIsland)
• Removes the schedule unit tests that validated ordering/level semantics
• Removes the re-exports of IslandSchedule/ScheduledIsland from pass::execution

Technical Notes: This PR is primarily an API/code deletion; downstream code must no longer rely on the removed scheduling helpers and should use the newer/superseding execution approach instead.

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[augmentcode]

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[codspeed-hq]

Merging this PR will not alter performance

✅ 24 untouched benchmarks
⏩ 56 skipped benchmarks¹

---

_{Comparing bm/be-524-hashql-remove-island-dag (5aa1fb4) with bm/be-525-hashql-remove-implicit-type-widening-into-num-for-int (7e018f0)}

Footnotes

1. 56 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩