rdmsm4x — ecs0lib pooled persistence prerequisite

Created the generic synchronous ECS0SQLitePool prerequisite in an isolated ecs0lib worktree; it is committed, test-verified, and awaiting shared-library owner publication rather than changing any consumer runtime.

Scope

• Host: rdmsm4x.
• Worktree: /Users/richh/dev/_worktrees/ecs0lib-tyrell-pooled-persistence-20260902.
• Branch: codex/ecs0lib-tyrell-pooled-persistence-20260902.
• Ticket: FEAT-20260902-25.
• Exact base: 90c3c6ddd6377be6012617d1934a5fbce5c028aa.
• Result commit: 1d82123f3a222489a319cec816c30a41a35a9dde.

Files and behavior

• Added Sources/ECS0Persistence/ECS0SQLitePool.swift with a bounded reader set, serialized writer, transaction/savepoint support, busy/foreign-key/WAL configuration, setup hook, and blocking close lifecycle.
• Added deterministic configuration, reader-bounding, writer-serialization, transaction, and close-lifecycle checks in Tests/ECS0LibTests/ECS0PersistenceTests.swift.
• Added docs/ECS0_POOLED_SQLITE.md, updated Sources/ECS0Persistence/ECS0Persistence.swift, and recorded resumable state in SESSION-STATE.md.
• Wrote the owner handoff at /Users/richh/dev/_handoff/ecs0lib-tyrell-pooled-persistence-20260902.md.

Validation

• swift build passed.
• Focused pool tests: 5 XCTest tests, 0 failures.
• Full suite: 189 XCTest tests plus 11 Swift Testing tests, 0 failures.
• ThreadSanitizer suite: 189 XCTest tests plus 11 Swift Testing tests, 0 failures and no ThreadSanitizer report.
• Aggregate and direct ECS0Persistence macOS Xcode builds passed.
• Aggregate iOS/tvOS/visionOS and direct persistence builds retain existing unrelated ISSUE-20260902-13 platform-availability failures; no unrelated remediation was attempted.

Preservation and rollback

• Canonical /Users/richh/dev/lib/ecs0lib was read-only. Its known fourteen ownerless untracked files remain present; the isolated manifest hash is recorded in the handoff.
• No canonical merge, remote publication, deployment, service change, credential access, or consumer change occurred.
• The owner can decline the isolated branch with no runtime rollback. If published later, revert commit 1d82123f3a222489a319cec816c30a41a35a9dde as one unit.

Outstanding owner action

The ecs0lib owner must review and explicitly accept or resolve the existing non-macOS aggregate build gate before deciding whether to publish the generic boundary. Consumer adoption, schema/migrations, release, and deployment remain out of scope.