Resolves #11976

Tests were reading gitignored, operator-mutable config.mjs overlays. This made the same commit behave differently across checkouts and allowed a direct template import plus a transitive overlay import to register the same Neo config class twice. The corrected test harness now resolves one committed template graph, keeps imported reactive Providers read-only, and uses fresh disposable Provider instances for config permutations.

Evidence: L2 (resolver runtime probes, one-worker shared-state topology, config-authority lint, and unified integration) → L2 required (all runtime ACs are test-harness-local). No residuals.

Deltas from ticket

• Adds one Playwright preload boundary that redirects only checkout-local ai/**/config.mjs imports with a committed sibling template. Relative, absolute, file-URL, and neo.mjs/ specifiers are covered; outside-checkout paths, tracked configs without a template, and disposable child repositories pass through.
• Loads that boundary before every Playwright mode and inherits it into descendant Node processes. Direct executable test imports were migrated for source honesty; the resolver closes transitive production-import gaps.
• Migrates the 112 AST-visible overlay imports plus the executed child-source import identified by the ticket. Three remaining overlay imports execute only inside disposable deployment repositories and intentionally test generated-overlay runtime behavior.
• Deletes the former Tier-1 and Knowledge Base defaults fixtures. They materialized reactive Provider proxies into frozen plain objects, violating ADR-0019 B1 and losing hierarchical/inherited state. Canonical assertions now read the committed template Provider directly; permutations create and destroy isolated ConfigProvider instances.
• Extends the target-zero config SSOT lint to reject test-side Provider-derived exports and direct Provider re-exports while allowing invocation-time direct reads. No snapshot or Provider-export baseline escape hatch exists.
• Corrects the source-path absence tests: the old delete operations were ineffective because the hierarchical proxy has no delete trap. Missing keys and a missing sourcePaths namespace are now constructed honestly on disposable Providers.
• Routes template-derived Chroma, SQLite telemetry, WAL, handoff, route-ledger, recovery, and log writes into disposable per-runner/per-worker storage.
• Repairs shared-worker isolation defects exposed by the unified template graph: bounded graph cleanup, restored singleton seams, exact fixture removal, and an explicit canonical-frontier prerequisite for the public archive-recall spec.

Config-template impact

• ai/config.template.mjs: adds engines.chroma.useUnitTestDatabase and engines.chroma.useTestHarness; engines.chroma.useTestDatabase becomes their computed effective selector. Existing host, port, and dataDir consumers remain unchanged.
• Memory Core: adds storagePaths.useUnitTestDatabase and storagePaths.useTestHarness; graph, collection, WAL, handoff, and route-ledger formulas use the effective test boundary.
• Knowledge Base and Neural Link: split memoryCoreDbPath into production/test leaves plus unit/Playwright selectors, while preserving memoryCoreDbPath as the computed consumer surface.
• Existing ignored operator overlays are not copied, overwritten, or migrated by this PR. Runtime production values therefore do not change. A future explicit config migration receives the new template shape; no MCP or harness restart is required for this test-only boundary.

Test Evidence

• Exact rebased head d14006865d: focused Provider/config/lint/RecoveryActuator/SourcePaths cluster, one worker — 126/126 passed.
• Exact rebased head d14006865d: node ai/scripts/lint/lint-config-template-ssot.mjs — pass; zero test overlay imports and zero test config-authority violations.
• Exact rebased head d14006865d: node buildScripts/util/check-aiconfig-test-mutation.mjs — pass; 801 files scanned, zero new violations.
• Exact rebased head d14006865d: npm run agent-preflight -- --no-fix <changed files> and git diff origin/dev...HEAD --check — pass.
• Earlier pre-correction head 82a46ae542: resolver/lint/config and spawned-process cluster — 104 passed; shared-state regression clusters — 209/209, 56/56, and the exact GraphService → MailboxService → PublicRecall one-worker chain 149/149.
• Earlier pre-correction head 82a46ae542: full unit normal topology — 7,164 passed; exact CI topology — 7,032 passed with four local sandbox-denied lifecycle writes subsequently isolated green 26/26; unified integration — 5 runnable passed, 45 deployment-gated skipped. Fresh GitHub CI will revalidate the rebased correction head.
• Whitebox E2E and local-model-only coverage: None found; this PR changes Node/Playwright test resolution and config isolation, not an app or model-execution surface.

Post-Merge Validation

• Confirm GitHub unit, integration-unified, CodeQL, and config-template SSOT checks are green on the merge candidate.
• In a clean checkout with customized ignored overlays, run a focused unit spec and verify the overlay bytes remain unchanged while direct and transitive config imports resolve to the same committed template singleton.
• Confirm no generated config migration or live MCP/harness restart is needed; this PR changes Playwright resolution only.

Evolution

The first implementation replaced hand-copied defaults with frozen snapshots of Provider.data. That preserved the wrong abstraction: Provider.data is a hierarchical reactive proxy, not a flat object, and snapshotting it created another authority while omitting inherited state. The correction removes the fixtures entirely, moves mutations to disposable Providers, and adds a narrow mechanical guard for the exact exported-snapshot/re-export recurrence.

Authored by Euclid (GPT-5.6 Sol Ultra, Codex Desktop). Session 837ad74b-c2d2-413d-9aab-b7165a93a82a.