extractor: standalone/entailment/selection doctrines in EXTRACTION_CORE

Data analysis of the five-source corpus (490 nodes, 244 chains) found
three pathologies the goal-first core let through:

1. Narrative-adjacency chains — premises that occasioned rather than
   entailed conclusions (concentrated in the polemical sources).
2. Session-scaffolding minted as knowledge — the source's own axiom
   numbering (A1/F2/UT2), arc labels ('the crux') persisted as nodes.
3. Full-discourse volume — glossary and argument-arc material at equal
   rank with load-bearing ideas (~200 nodes per source).

Three doctrine lines, same terse register as the core:
- entailment is the only link that earns a chain; historical/narrative
  connections keep their pieces as bare propositions or drop them
- load-bearing ideas only (what a reference on the subject would teach)
- propositions must stand alone for a reader who never saw the source;
  no leaning on the source's own scaffolding

Substring pins for all three; shared by session + notes extractors by
construction.

tests/extraction.test.ts

@@ -1184,6 +1184,10 @@ describe("the extractor redesign (owner, 2026-09-30): chains are the deliverable
 		// The core carries the goal + submission mechanics.
 		assert.match(EXTRACTION_CORE, /JOINTLY entail a conclusion/);
 		assert.match(EXTRACTION_CORE, /for the same conclusion are separate chains/);
+		assert.match(EXTRACTION_CORE, /Entailment is the only link that earns a chain/);
+		assert.match(EXTRACTION_CORE, /what a reference on it would teach/);
+		assert.match(EXTRACTION_CORE, /stand alone for a reader who never saw this source/);
+		assert.match(EXTRACTION_CORE, /may not lean on the source's own scaffolding/);
 		assert.match(EXTRACTION_CORE, /SUBMIT with one submit_findings call/);
 		assert.match(EXTRACTION_CORE, /"chains": \[\] when the source makes no arguments/);