Knowledge, notes, memory and skills, and a harness to make them used

Four places a model can reach for, differing in who writes a record and how it
gets in front of the model.

**Knowledge** is uploaded by a person and searched by the model. It goes through
`services/files.py:prepare` — the same pipeline as a chat attachment — so the
same PDF produces the same text whichever way it arrived, and `Document` carries
the same content columns as `Attachment` for the same reason.

**Notes** are written by the model and edited by you. Too long to inject, so
they are searched.

**Memory** is short facts, and every one of them goes into every request. That
single decision is where the rest of its design comes from: records are capped
short, the block has a budget, there is no search tool because the model is
already looking at them, and they are not shareable — a record about a person is
not content to hand round.

**Skills** are saved procedures. Only the name and description are injected; the
body is fetched when the model decides one applies, which is what makes a
hundred skills affordable. A model may write and revise its own — the safety
story is not a gate but a record: every revision is kept, attributed and
revertible. A model that has just read a hostile page can save a skill that
outlives the conversation, and the honest mitigation is that it is visible and
undoable rather than that it was prevented.

**The harness** is why any of it gets used. A model handed a tools array
ignores it and answers from recall, because nothing in the request suggests
otherwise. `services/harness.py` assembles a preamble from what this chat
actually has: when to reach for each tool, the memories, the skill index.

This is an exception to "system prompts are precedence, not concatenation", and
a deliberate one. That rule governs the three *authored* layers and is
untouched — exactly one still wins. The harness is a different axis: it
describes the machinery rather than the behaviour, nobody authored it, and there
is nothing for it to disagree with. It is prepended to whichever authored prompt
won, in one system message, since several endpoints reject a second.

Supporting changes:

- **Sharing**, in one helper. `visible_to()` is the only definition of who can
  see a library item and every listing and tool goes through it. Sharing grants
  *reading*; two people editing one note with no history and no merge is worse
  than copying it. **Administrators do not bypass this** — they bypass
  permissions elsewhere because an admin can grant themselves those anyway, but
  reading somebody's private notes is a different act.
- **FTS5**, created by `db/migrations.py:ensure_fts` with the triggers an
  external-content index needs. Idempotent, like the column sync beside it.
  Terms are ANDed and then ORed: the caller is usually a model writing a whole
  question, and requiring every word loses the match on one absent term.
- **The attach button is a menu** — file, image, a web page, or a document from
  the library. Attaching a document copies it, because history must not change
  when a document is edited later.
- **A URL fetcher with an SSRF guard.** This server can reach the router, the
  other services on the box and LLeMbas itself, and the address can come from a
  model. Private ranges are refused *after resolution* and redirects are followed
  by hand so every hop is checked. An admin can open it deliberately.
- **Model capabilities split** into protocol support and a toggle per built-in
  tool. Rows predating the split have no `tool_*` keys, and absent counts as on
  when `tools` is on — otherwise an upgrade silently takes web search away from
  every model already configured for it.

Also fixes the test fixture, which built the schema with `create_all` and so ran
against a database without the FTS tables production has; it now runs
`sync_schema`, the same path startup takes.

430 tests, ruff clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lembas/db/migrations.py

@@ -96,6 +96,93 @@ def _add_column_sql(table: Table, column: Column, dialect) -> str | None:
     return " ".join(parts)
 
 
+# --- Full-text search --------------------------------------------------------
+# The library stores are searched rather than listed, and LIKE over a few
+# hundred documents ranks nothing and matches badly. SQLite ships FTS5, so the
+# index costs no dependency and works offline like everything else here.
+#
+# These are the one part of the schema this module's model-diffing cannot
+# derive: an FTS5 virtual table is not a SQLAlchemy model, has no columns to
+# compare, and needs triggers to stay in step with the table it shadows. So it
+# is written out -- but written out *idempotently*, with IF NOT EXISTS
+# throughout, which keeps it the same kind of thing as the column sync: run it
+# at every startup and it converges.
+#
+# `content=` makes each index external-content: the text is not stored twice,
+# and the triggers below are what the FTS5 documentation calls for to keep an
+# external-content index correct through updates and deletes.
+FTS_INDEXES: tuple[tuple[str, str, tuple[str, ...]], ...] = (
+    ("documents_fts", "documents", ("title", "description", "extracted_text")),
+    ("notes_fts", "notes", ("title", "body")),
+    ("skills_fts", "skills", ("name", "description", "body")),
+)
+
+
+def _fts_statements(index: str, table: str, columns: tuple[str, ...]) -> list[str]:
+    # `id` rides along UNINDEXED so a match can be turned straight back into an
+    # ORM row. The alternative is joining on rowid, which SQLAlchemy models do
+    # not expose and which changes under VACUUM.
+    columns = ("id", *columns)
+    column_list = ", ".join(columns)
+    declared = ", ".join(
+        f"{name} UNINDEXED" if name == "id" else name for name in columns
+    )
+    new_values = ", ".join(f"new.{name}" for name in columns)
+    old_values = ", ".join(f"old.{name}" for name in columns)
+
+    return [
+        f"CREATE VIRTUAL TABLE IF NOT EXISTS {index} USING fts5("
+        f"{declared}, content='{table}', content_rowid='rowid')",
+        # 'delete' rows carry the old values because an external-content index
+        # cannot look them up itself once the source row has gone.
+        f"""CREATE TRIGGER IF NOT EXISTS {index}_ai AFTER INSERT ON {table} BEGIN
+              INSERT INTO {index}(rowid, {column_list}) VALUES (new.rowid, {new_values});
+            END""",
+        f"""CREATE TRIGGER IF NOT EXISTS {index}_ad AFTER DELETE ON {table} BEGIN
+              INSERT INTO {index}({index}, rowid, {column_list})
+              VALUES ('delete', old.rowid, {old_values});
+            END""",
+        f"""CREATE TRIGGER IF NOT EXISTS {index}_au AFTER UPDATE ON {table} BEGIN
+              INSERT INTO {index}({index}, rowid, {column_list})
+              VALUES ('delete', old.rowid, {old_values});
+              INSERT INTO {index}(rowid, {column_list}) VALUES (new.rowid, {new_values});
+            END""",
+    ]
+
+
+def ensure_fts(engine: Engine) -> list[str]:
+    """Create the search indexes and their triggers if they are missing.
+
+    Returns the indexes it created. A failure here is logged and swallowed:
+    search degrading to "finds nothing" is bad, but it is much better than the
+    application refusing to start.
+    """
+    created: list[str] = []
+    inspector = inspect(engine)
+    known = set(inspector.get_table_names())
+
+    with engine.begin() as connection:
+        for index, table, columns in FTS_INDEXES:
+            if table not in known:
+                continue
+            fresh = index not in known
+            for statement in _fts_statements(index, table, columns):
+                connection.execute(text(statement))
+            if fresh:
+                # Backfill anything already in the table. Only on creation --
+                # the triggers keep it current from then on.
+                column_list = ", ".join(("id", *columns))
+                connection.execute(
+                    text(
+                        f"INSERT INTO {index}(rowid, {column_list}) "
+                        f"SELECT rowid, {column_list} FROM {table}"
+                    )
+                )
+                created.append(index)
+
+    return created
+
+
 def sync_schema(engine: Engine) -> list[str]:
     """Bring the database up to the declared schema. Returns what it changed."""
     import lembas.db.models  # noqa: F401  (registers every table on the metadata)
@@ -125,6 +212,12 @@ def sync_schema(engine: Engine) -> list[str]:
                 changes.append(f"add column {table.name}.{column.name}")
                 log.info("schema: %s", statement)
 
+    try:
+        for index in ensure_fts(engine):
+            changes.append(f"create search index {index}")
+    except Exception:  # noqa: BLE001 - search is not worth refusing to start over
+        log.exception("could not create the full-text search indexes")
+
     if changes:
         log.info("schema synchronised: %d change(s)", len(changes))
     for step in MANUAL_STEPS: