Give the system a directory: ask who knows, then ask them

A memory system that only answers from its own store is a filing cabinet,
not a partner. The transactive rule the project is named for — not knowing
is fine when you know who does — needed a holder registry, a directory
query, and a referral that never leaks the text it may not read.

- schema v5 adds `holders` (person/agent/service, declared topics, contact).
  A holder with memories exists whether or not anybody registered them; the
  registry adds reachability, it does not grant existence.
- `who_knows` ranks holders by their own memories and is deliberately NOT
  filtered by visibility: "she knows" is the answer. The answer is filtered.
- `ask` searches the asker's visible scope first (hop 0), then walks the
  directory with a visited set and a hop budget. Three terminal states:
  answered, referred, no_holder_knows. Nobody knowing is a result, not an error.
- Confidence is ordinal, not calibrated: relative strength, coverage, and
  declared topics. Every hit carries the raw numbers and the basis lines that
  produced the score, so a ranking can be argued with.
- Faces: HTTP (/api/holders, /api/who_knows, /api/ask), CLI (holders,
  holder-set, holder-rm, who-knows, ask), MCP (who_knows, ask, list_holders).

Four bugs found by running the thing, not by reading it:
- FTS5 refuses bm25() inside MAX(); the aggregate uses FTS5's own `rank` column.
- A CJK question is longer than the sentence that answers it, so the whole-run
  phrase matched nothing. The query now ORs adjacent bigram phrases; adjacency
  is kept, equal length is not. Latin path untouched, baseline unaffected.
- The hop budget counted the asker as a hop, so max_hops=1 asked nobody.
- A second, stricter readability test in _answered() disagreed with the SQL
  visibility clause and hid a memory the asker was allowed to read. The SQL
  clause is the only authority now.

A method named `list` shadowed the builtin inside its own class and made
mypy reject the return annotation; renamed rather than cast around it.

Proof: 155 pytest, 12 Go tests, ruff and mypy clean on touched files, pyright
ledger unchanged at 62, and scripts/mcp_write_smoke.sh drives two principals
on one SQLite file — the husband asks through MCP, gets `referred` with his
wife's contact channel, and her private sentence appears nowhere in the reply.

backend/src/ely_eye/migrations.py

@@ -14,7 +14,7 @@ import sqlite3
 
 from .text_index import index_text
 
-SCHEMA_VERSION = 4
+SCHEMA_VERSION = 5
 
 ATOM_COLUMNS_V2 = """
     atom_id TEXT PRIMARY KEY,
@@ -82,6 +82,21 @@ _BASE_TABLES = """
         mounted_at TEXT NOT NULL
     );
 
+    -- The directory of who may hold or answer a memory. A transactive system answers
+    -- "who knows this?" before it answers "what is this?", and it cannot do that without
+    -- an entity to point at. Contact details are free-form on purpose: the transport is
+    -- whoever wired this store together, not the schema.
+    CREATE TABLE IF NOT EXISTS holders (
+        holder_id TEXT PRIMARY KEY,
+        name TEXT NOT NULL DEFAULT '',
+        kind TEXT NOT NULL DEFAULT 'person'
+            CHECK (kind IN ('person', 'agent', 'service')),
+        knows_about_json TEXT NOT NULL DEFAULT '[]',
+        contact_json TEXT NOT NULL DEFAULT '{}',
+        created_at TEXT NOT NULL,
+        updated_at TEXT NOT NULL
+    );
+
     CREATE TABLE IF NOT EXISTS cache_events (
         id INTEGER PRIMARY KEY AUTOINCREMENT,
         ts TEXT NOT NULL,