fix(runtime): end a loop body's own performance of the node a terminate names

[devin-ai-integration]

What and why

A loop body reached by several tokens runs one performance of the body per token. terminate slow; inside it reached the paused slow performances of the other loop performances too, because a statement node's body performed its nodes directly in the enclosing frame: ActionExecutor.ongoing(parent, node) filters by parent and node only, so every loop performance's slow shared one parent. The same model written with succession (a stated flow) already scoped it to its own and failed with performance already ended.

Root-cause fix: a token's step of a statement node (loop, if, assignment, send, terminate written as a statement) is now a transparent performance owning what its body performs.

stepStatementNode:  step := beginStatementStep(token.frame, node)   // body: true, label = frame.describe()
statementWork.perform: executeStatementBody(step, graph); step.ended = true
actionStmtHost.around() = step ?? perf   // performNode / performBlockFlow / terminate resolve from it
reachableFrames: visits the step of a token's statementWork  // snapshots, held images, state keys

Feature reads and writes still go to the enclosing performance (the body's lexical frames are unchanged), and diagnostics name the same performances as before.

Fixtures. The two fixtures that relied on the cross-loop reach are redesigned so each still ends a paused performance in its own scope:

• action_terminate_names_node_of_paused_bodies: each loop body's slow naps while a watch inside it, due first, runs terminate slow;.
• action_terminate_names_node_performing_action: the same, with slow performing Nap.

New action_terminate_names_node_of_its_own_loop_performance pins the cross-loop case: the third loop performance's slow ends itself while the first two nap on and complete (napped = 2).

Specification basis

Actions::TerminateAction performs terminateOccurrence : destroy on terminatedOccurrence. OccurrenceFunctions::destroy connects occ.endShot to the destroy performance with HappensDuring, so the occurrence must end during the terminate. An occurrence whose endShot already happened cannot satisfy that, so terminating an ended performance stays the typed ErrPerformanceEnded, not a no-op. A loop body's terminate slow designates the slow of the body performance it runs in; each body performance owns its own.

The terminate row in docs/project/spec-compliance.md is narrowed to the performances the statement runs within, and cites the new fixtures and robustness cases. It stays ✅ Faithful.

How it was verified

• robustness_terminate_nested_test.go (TestRuntimeRobustnessTerminateNestedFlowTarget):
  • own slow already ended while the others are paused → ErrPerformanceEnded;
  • own-scope terminate leaves the other loop performances' naps running;
  • terminate ordered before its node began → ErrTerminateTarget.
• Conformance and trace goldens for the three fixtures.
• go build ./..., go vet ./... and gofmt -l . are clean. go test ./... passes with the corpora downloaded, except tests/identity TestPilotLibraryXMI: that XMI isn't downloaded locally while its require variable is set.
• make docs-check and python3 scripts/changelog.py check pass.

Checklist

• make test and make lint pass locally (go test ./...; race run left to CI)
• Tests added or updated for the change
• Documentation extended where it already covers the surface (see CONTRIBUTING.md)
• Changelog entry added as changes/unreleased/<slug>.<section>.md, not as an edit to CHANGELOG.md
• baselines regenerated and make docs-counts run if a gate count moved (compliance rows need nothing: the census is counted at docs build)
• No internal work-item labels (waves, slices, F4, K5) in the body, docs, or changelog

Link to Devin session: https://nasa-jpl-demo.devinenterprise.com/sessions/5344039f62464badb7a0a648e6384b08
Open in Devin Desktop: https://nasa-jpl-demo.devinenterprise.com/desktop/session/5344039f62464badb7a0a648e6384b08?variant=devin
Requested by: @HuiJun

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

[devin-ai-integration]

This branch now conflicts with develop. Conflicting files, and the merged PRs that changed them:

• internal/exec/runtime/action_statements.go (fix(runtime): explore every order of unordered statements in calc, constraint and case bodies #864, feat(migrate): write object flows as succession flows and carry values through control nodes #856)
• internal/exec/runtime/testdata/conformance/action_terminate_names_node_of_paused_bodies.trace.golden (fix(runtime): name loop, if and statement nodes in traces by what they do #848)
• internal/exec/runtime/testdata/conformance/action_terminate_names_node_performing_action.trace.golden (fix(runtime): name loop, if and statement nodes in traces by what they do #848)

To resolve: merge current develop into this branch with an ordinary merge commit (no rebase or force-push).
Reconcile the code conflicts with #864's statement-order scheduling (calc, constraint and case-step bodies) rather than taking one side; a conflict that needs a design decision should be raised on this PR, not guessed.
The two trace goldens moved because #848 renamed nodes descriptively; regenerate them with go test -run TestExecutionTrace ./internal/exec/runtime -update-traces and check that only the intended lines differ.

Planned merge order for the execution PRs: #844 → #850 → #838 → (#851 → #853 → #857) → #830 → #833 → #842 → #837 → #834 → #816.

Re-run the full gate (go build ./..., go vet ./..., gofmt -l ., make lint, make docs-check, go test ./...) and wait for green CI before marking ready.

[devin-ai-integration]

Hold on pushes: please don't push to this branch, including develop merges or empty commits to retrigger CI, until a maintainer says the CI runners are free. Prepare the conflict resolution locally and push it then.