aiConfig Provider singleton mutated without restore across ~11 test setups — add snapshot/restore isolation

Context

PR #12423 review surfaced (operator-flagged) a widespread test anti-pattern: specs mutate the aiConfig Provider singleton in their setup blocks without restoring it. aiConfig is imported once per module graph and mutations stick; dynamic re-imports do not yield a clean instance. This is a latent cross-test corruption hazard.

The Problem

~11 specs write aiConfig.storagePaths.graph (and .autoIngestFileSystem, .engines.chroma.database) in beforeEach / describe-setup without restore, e.g.: GraphService.spec, MC ChromaManager.spec, McpServerToolLimits.spec, WriteSideInvariant.spec, SessionSummarization.spec, MC Server.spec, SessionService.spec / SessionService.ResumeValidation.spec, MemorySessionIngestor.spec, ConceptIngestor.spec, QueryReRanker.spec, DreamService.spec.

Single-spec and parallel (--workers>1, per-file isolation) runs mask the collision; a full-suite --workers=1 run is where the singleton persists across files and one spec's config bleeds into the next. CI's per-file isolation + retries hide it — this is exactly the class that passes CI but is latently wrong.

The Architectural Reality

• aiConfig is a Neo Provider singleton (one instance per module graph; not reconstructed by re-import).
• Correct precedent in-tree: test/playwright/unit/ai/mcp/server/shared/services/DestructiveOperationGuard.spec.mjs:223-234 captures originalGraphPath = aiConfig.storagePaths.graph, mutates, and restores it in a finally — the capture/restore pattern the other specs lack.

The Fix (lead prescription)

A shared test-isolation helper that snapshots the mutated aiConfig keys at setup and restores them in afterEach/afterAll (capture/restore), adopted across the ~11 specs. (Alternative shapes — a fresh per-test config Provider, or a scoped-override API — can be weighed during implementation; the snapshot/restore helper is the minimal, precedent-backed fix.)

Acceptance Criteria

• A shared helper snapshots + restores the mutated aiConfig keys around each affected spec.
• All enumerated specs adopt it; no unrestored aiConfig.* writes remain in their setup.
• Negative isolation test: a representative full-suite --workers=1 run is green with no cross-spec config bleed.

Out of Scope

• Redesigning aiConfig Provider semantics.
• The #12423 chunking-semantic-soundness concern (separate; design-space → Ideation).

Decision Record impact

none.

Related

• Surfaced in: PR #12423 review.
• Correct-pattern precedent: DestructiveOperationGuard.spec.

Origin Session ID: 4cfb33e9-9d3a-4af7-afa8-e3d71ed4bcc7 Retrieval Hint: "aiConfig Provider singleton test mutation no restore cross-test pollution --workers=1 snapshot restore helper #12423"