docs: changelog, CONCEPTS research-pipeline cluster, grounding solution doc

CHANGELOG covers the narrative lens (Added) and head-token grounding
fix (Fixed). CONCEPTS.md gains a Research pipeline cluster (Primary
entity, Intent modifier, Entity grounding, Keyless path,
Comment-enrichment slots). New docs/solutions/logic-errors/ entry
captures the false-demotion bug, the rejected alternatives, and the
shared-helper prevention rule.

CONCEPTS.md

@@ -16,6 +16,30 @@ The Python script (`scripts/last30days.py`) the Skill's SKILL.md invokes to do t
 
 The agent runtime that loads Skills and invokes them on the user's behalf. Claude Code is the most common Harness for this Skill but not the only one — Codex, Cursor, GitHub Copilot, Gemini CLI, and the rest of the Agent Skills ecosystem also count. "Multi-harness" describes a Skill that works correctly across every Harness it installs into; features written without multi-harness awareness (e.g., engine flags with no SKILL.md integration, or paths hardcoded to one Harness's install layout) regress on Harnesses other than the one they were tested against.
 
+## Research pipeline
+
+### Primary entity
+
+The brand or proper-noun core of a research topic — the topic with its Intent modifier stripped. It is what the research is *about*, as distinct from how the user phrased the search.
+
+### Intent modifier
+
+A trailing word or phrase in a topic that expresses what the user wants to know rather than what the topic is ("review", "use cases", "pricing"). Stripped when deriving the Primary entity.
+
+### Entity grounding
+
+The check that a candidate item plausibly mentions the Primary entity before final ranking. Grounding keys on the head token (first word) of the Primary entity rather than the full phrase — trailing words are usually search descriptors, so requiring them falsely demotes on-entity items.
+
+An item that fails grounding receives a decisive entity-miss demotion, designed so engagement cannot rescue off-entity content. Because the demotion is decisive, the grounding bar is deliberately conservative: its failure modes degrade toward "no penalty," never toward burying on-entity signal.
+
+### Keyless path
+
+The research flow available with no API keys: source data is gathered by scraping and RSS rather than authenticated APIs, and ranking falls back to local scoring instead of LLM-based reranking. This is the free tier of the Skill; lexical quality safeguards like Entity grounding matter most here, because no LLM is available to judge relevance semantically.
+
+### Comment-enrichment slots
+
+The small, depth-dependent budget of Reddit posts whose comments get fetched in the Keyless path. Slot selection is relevance-aware: posts that pass Entity grounding claim slots first, so the budget is not spent on high-engagement posts that final ranking will demote anyway.
+
 ## Distribution
 
 ### Beta channel