fix(core-initializers): do not clean up artefacts while the registry is being written

[delchev]

Fixes the intermittent IntentCrossModelFieldRetirementIT failure on master's postgres leg (e.g. run 31315813251).

What actually happens

A publish replaces a registry collection by deleting it and copying it back milliseconds later — both steps inside a single request. A synchronization pass that walks into that hole finds the sources gone and permanently deletes their artefact rows. From the failing run's log:

15:38:35.032  PublisherService   Unpublished collection: /registry/public/retire-owner/gen/invoices
15:38:35.676  JavaSynchronizer   Removing Java artefact [/retire-owner/gen/invoices/api/invoice/InvoiceController.java]
15:38:35.717  JavaSynchronizer   Removing Java artefact [/retire-owner/gen/invoices/data/invoice/InvoiceEntity.java]
   … four more …
15:38:35.736  PublisherService   Published collection: [/users/admin/workspace/retire-owner] → /registry/public/retire-owner

The files were back 21 ms after the last deletion, but their artefacts were gone. Reconcilers that rebuild from the whole artefact set then work from a half-empty registry — for client Java that is one javac batch over a source set whose cross-references cannot resolve:

Compiled batch: [8] units, [6] class file(s); [2] failed
   javac error … package gen.invoices.data.invoice does not exist
Compiled batch: [11] units, [0] class file(s); [11] failed   ← cascade of "cannot find symbol"

Zero bytecode, so the owner's InvoiceController was never registered and the test's 60 s poll saw nothing but 404s. Nothing re-triggered a rebuild, so the instance stayed dead.

The fix

Defer cleanup when a registry-mutating request was in flight while the pass ran. A new RegistryMutationTracker (core-base) counts those requests; a filter marks the publisher and workspace endpoints. Only mutating methods count — the IDE polls those endpoints with GET constantly — and the filter is registered explicitly through a FilterRegistrationBean so Boot does not map it to every request: a write through a generated application's REST controller is not a registry mutation.

The question is deliberately "was a client writing", not "did the registry change". My first attempt keyed on the file-system watcher flag, and SynchronizationInitializerDeletedTest caught it immediately: the watcher reports a genuine deletion exactly like a publish, so that version delayed every deletion by one pass. The tracker distinguishes the two with no timing heuristic at all.

Stop compiling a batch we already know is incomplete. JavaSynchronizer.rebuildAll used to silently skip a registered source whose file was momentarily missing and compile the rest; it now defers the rebuild to the next cycle, by when either the file is back or the orchestrator has dropped the artefact.

Rejected alternatives: a two-consecutive-passes rule delays every deletion (and breaks the delete-assertion tests), and a lock inside PublisherService cannot span the delete and the copy when a handler issues them separately.

Verification

SynchronizerCleanupRaceIT drives passes with a publish in flight. It does not assume a pass ran — a probe artefact published during the window must appear first, which is the proof a full pass completed (processSynchronizers() silently skips when another run holds the slot; an earlier version of this test passed against the unfixed code precisely because of that). It then asserts the missing source's artefact survived, and that a genuine deletion is still reconciled in a single forced call.

• With the fix: SynchronizerCleanupRaceIT, IntentCrossModelFieldRetirementIT, RoleSynchronizerCleanupIT, JavaEngineIT (5/5), and core-initializers' unit tests (5/5, incl. SynchronizationInitializerDeletedTest) all green.
• With the deferral disabled: SynchronizerCleanupRaceIT fails with [an artefact whose source vanished mid-publish must not be cleaned up] Expecting actual not to be empty.

mvn formatter:validate and the release-profile javadoc build pass on all touched modules.

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