fix(storage): publish ER position after persistence

[HandSonic]

Related issue

N/A - no matching issue was found.

Summary

ERPositionStorage.savePosition modified the live cached object before the base storage write completed. A write failure therefore left memory showing the new position while disk and a reloaded instance retained the old value. This change builds a detached candidate list, persists it first, and publishes only the successful replacement/generated ID.

Affected surfaces

• Frontend / Web
• Backend / API / Storage
• Database plugin / Driver
• JCEF / Desktop packaging
• CI / Build / Release
• Documentation only

Verification

• Reproduced on main: 5 ER tests ran, with one failure showing the new in-memory position after a failed write while disk/reload retained the old value.
• Latest-main integration tests and owning reactor package passed: storage 71, tools 77, domain-api 27; 175 total, zero failures/errors/skips.
• Command: mvn -B -ntp -f chat2db-community-server/pom.xml -pl :chat2db-community-storage -am -Dmaven.test.skip=false -DskipTests=false '-Dsurefire.includes=**/*Test.java' -Dsurefire.failIfNoSpecifiedTests=false -Dmaven.test.failure.ignore=false package. Test JVM home/temp directories were isolated.
• Executable backend package and Playwright CLI verification passed using two isolated SQLite datasources: real mouse drags, consecutive layout updates, refresh, backend restart, reset layout and retry after permission recovery. Browser node coordinates were compared with actual save requests and persisted positions.
• Real storage-directory write denial covered first insertion and replacement: memory and file bytes were unchanged, other datasource layouts were preserved, and refresh restored the persisted layout.
• Zoom, fit-view and Escape did not write positions. The flow auto-saves and has no save-cancellation dialog.
• Both PR files are byte-identical to the Web-tested version; newer main changes are outside the ER persistence path. New-head CI is available in PR checks.
• Existing frontend limitation observed: save failures are not shown to the user, and the optimistic position remains until refresh. The unchanged frontend does not handle the rejected promise; this is recorded separately from the storage fix.

Risk and compatibility

• Public API or stored data: Existing JSON format and method signatures are unchanged.
• Database or driver compatibility: N/A.
• Network, privacy, or security: N/A.
• Community / Local / Pro boundary: Shared Community ER layout storage.
• Backward compatibility: Successful inserts/updates preserve existing lookup keys and IDs.

Reviewer map

• Start here: ERPositionStorage.savePosition and its failure regression test.
• Failure condition: a failed write changes memory, caller ID, file bytes, or reload state.
• Rollback or disable path: Revert this PR; no migration is required.

Contributor declaration

• I linked the Issue that defines this change.
• I tested the affected behavior and reported the actual results above.
• I did not include credentials, private data, or generated build output.
• I disclosed substantial AI assistance below, or this PR contains no substantial AI-generated code.

AI assistance: OpenAI Codex assisted with diagnosis, implementation, deterministic tests, verification, and adversarial review.