fix: D32 layer-2 grounds against the union of source-derived texts

[fazpu]

Urgent fix from the GLM-5.2 smoke, diagnosed by the #161 loss ledger: 371 of 411 grounding rejections were correct decontextualizations killed by wrong attribution labels — the model adds "Caroline" (verbatim in the target chunk's turn line) but tags it header/prefix, and the per-element membership check rejects it. 27 claims survived from 19 documents.

The fix: layer-2 membership checks the union of source-derived bundle texts (target chunk, header, same-section neighbours, stored prefix); the model's source_kind stays recorded as advisory provenance but cannot reject a grounded addition. Section summaries remain outside the union — the fact-injection defense is unchanged and the poison probes still bite (asserted). The prompt now states in-chunk text needs no added_context at all. E2_EXTRACTOR_VERSION → 07g:union-grounding-1; dated amendments in the E2/E3 design §3.3 and D32.

Review: Grok APPROVE (2 MINOR / 2 NIT; the docs-honesty MINOR fixed in the second commit — the union excludes summaries, not the prefix, which is D79's accepted second-order channel). Final review by Claude. Fast gate local; full matrix in CI.

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File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
src/rememberstack/workers
e1.py
e2.py
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