Remove array-route leftovers and #854 heap harnesses after the journal-fed send route #3848

Problem

#854 made the journal-fed source route the only send route and deleted the array send route and its enforcement. Code that only served the old array route, plus measurement harnesses from the #854 investigation, is still in the tree. The removal was left out of #854 to keep that PR's diff reviewable.

Candidates

Each item needs a caller check before deletion. Anything still reachable from a product path stays.

Provider paths for calls without requestRows

• packages/providers/src/utils/collectContents.ts and its users in loadBalancing/preparedPromptOptions.ts. LoadBalancingProvider still has a collect-and-replay branch for calls that arrive without requestRows.
• The Responses content filler used when a call carries contents instead of rows.
• The Anthropic and OpenAI chat projectPromptEnvelope array branches.
• packages/agents/src/core/DirectMessageProcessor.ts seems to be the last production caller that sends a materialized contents array. Moving it onto request rows would let the branches above go.

Test oracles

• The in-memory OneShot/MiddleOut compress() paths in packages/agents/src/compression. Product compression runs through the disk runners. The in-memory versions survive as byte-equivalence oracles for scripts/tests/oneshot-summary-body.test.ts and middleout-summary-body.test.ts. They belong in test support, not product source.

Heap and owner-count harnesses
The repeated-turn retained-heap proof packages/agents/src/core/__tests__/journal-retained-growth.test.ts (400 turns, with a trap that must fail) now covers memory retention. These older harnesses take statistical heap samples or owner counts, and should either be deleted or cut down to plain behavioural assertions:

• packages/cli/src/services/wholepeak.test.ts, wholememory-probe.test.ts, wholememory-targets.test.ts, wholememory-media-peak.test.ts and their support modules.
• The remaining scripts/tests/*-memory-child.ts workloads and their parent tests.
• packages/test-utils retained-growth helpers, if nothing else uses them.
• The streamprocessor-retained* owner census tests in packages/agents/src/core.

Related: #3298 (older dead provider legacy paths).

Acceptance

• Each removed path has no product callers. Show the grep or structural check in the PR.
• Request bodies are unchanged, verified by the providerBody*.p05b4 and source differential tests.
• Lint, typecheck and the full test suite stay green, with no thresholds relaxed.

Follow-up from #854.