BE-304: HashQL: Terminator placement based on capabilities

[indietyp]

🌟 What is the purpose of this PR?

Adds terminator placement analysis to the MIR execution planning pipeline. This complements statement placement by analyzing control flow edges rather than individual statements, determining which backend transitions are valid at each edge and their associated transfer costs.

🔍 What does this change?

• Introduces TransMatrix for encoding valid (source → destination) backend transitions per edge
• Adds TerminatorCostVec to collect transition matrices for all edges in a body
• Implements TerminatorPlacement analysis that computes costs based on:
  • Liveness analysis (which locals cross edges)
  • SCC detection (loop membership for Postgres restrictions)
  • Terminator-specific rules (GraphRead, SwitchInt, Goto)
• Moves execution/ module from pass/analysis/ to pass/ (organizational)
• Adds helper methods to BodyFootprint for computing average transfer costs

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?

• 162 unit/integration tests + 41 doc tests passing
• New snapshot tests for execution analysis integration scenarios
• New unit tests for island placement and interpreter traversal costs
• Existing CSP, splitting, and statement placement tests updated for allocator changes

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
hash	Ready	Preview, Comment	Feb 21, 2026 10:04pm
petrinaut	Ready	Preview	Feb 21, 2026 10:04pm

2 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
hashdotdesign	Ignored	Preview	Feb 21, 2026 10:04pm
hashdotdesign-tokens	Ignored	Preview	Feb 21, 2026 10:04pm

[cursor]

PR Summary

Medium Risk
Introduces new control-flow/back-end transition cost logic that will influence execution planning decisions; although well-tested, mistakes could change backend selection or produce overly conservative Cost::MAX transfers.

Overview
Adds terminator placement for MIR execution planning: a new TerminatorPlacement analysis computes, per control-flow edge, which backend transitions are allowed and their costs via a per-edge TransMatrix collected in TerminatorCostVec.

Transfer costs are derived from liveness + per-local BodyFootprint size estimates, with explicit transition rules for Goto/SwitchInt/GraphRead, plus Postgres restrictions (no incoming transitions; disabled in loops/self-loops). Execution-planning code is moved out of pass::analysis into pass::execution, Cost gains MAX and saturating_add, and size-estimation gains Estimate::eval and Footprint::average helpers (plus range/unit utilities) to support cost computation; adds list support to the rvalue! builder macro and snapshot/unit tests for the new analysis.

^{Written by Cursor Bugbot for commit 3927741. This will update automatically on new commits. Configure here.}

Your organization requires reapproval when changes are made, so Graphite has dismissed approvals. See the output of git range-diff at https://github.com/hashintel/hash/actions/runs/22184745507

[graphite-app]

Merge activity

• Feb 21, 1:37 AM UTC: Graphite rebased this pull request, because this pull request is set to merge when ready.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with Cloud Agents, enable Autofix in the Cursor dashboard.}