docs(context): add ingest identifier verification protocol

packages/context/skills/historic_sql_patterns/SKILL.md

@@ -18,6 +18,37 @@ Use this skill when the WorkUnit raw file is a `patterns-input/part-0001.json` s
 6. Set each evidence object's `rawPath` to the exact raw file path read in step 3.
 7. Stop after all pattern evidence has been emitted.
 
+Every join column mentioned in pattern descriptions must be verified via
+entity_details for both sides of the join.
+
+## Identifier Verification Protocol
+
+Before writing a wiki page or SL source on any topic:
+
+1. `discover_data({query: "<topic>"})` - see what wikis, SL sources, and raw
+   tables already exist. Prefer updating existing pages over creating new ones.
+
+Before emitting any `schema.table` or `schema.table.column` into a wiki body,
+SL source, `tables:` frontmatter, `sl_refs`, or `emit_unmapped_fallback`:
+
+2. `entity_details({connectionName, targets: [{display: "<identifier>"}]})` -
+   confirm the identifier resolves; inspect native types, FK/PK, and
+   sampleValues.
+3. For literal values from the source, such as status codes or plan tiers,
+   check whether they appear in `entity_details` sampleValues for the relevant
+   column. If sampleValues is short or the sample may have missed real values,
+   run a `sql_execution` probe:
+   `SELECT DISTINCT <col> FROM <ref> LIMIT 50`.
+4. If the candidate identifier still does not resolve, do one of:
+   - Use `sql_execution` with `SELECT 1 FROM <ref> LIMIT 0`. If it errors, the
+     identifier is fictional.
+   - Wrap the identifier in `[unverified - from <rawPath>]` in the wiki body,
+     citing the exact raw path that mentioned it.
+   - When recording `emit_unmapped_fallback` with `no_physical_table`, include
+     the failing probe error in `clarification`.
+5. Never copy `<schema>.<table>` placeholder strings from these instructions
+   into output.
+
 ## Evidence Shape
 
 Each call to `emit_historic_sql_evidence` must use this shape: