fix: clamp negative fromLine in get to avoid silent tail content

The query tool description tells agents to compute fromLine = line - 20
for context around a hit. For hits in lines 1 through 20 that yields a
negative fromLine, which propagated unchanged through:

  MCP get handler -> store.getDocumentBody -> Array.prototype.slice

A negative slice start offsets from the end of the array rather than
clamping to the beginning, so a top-of-file hit on a long document
returned an empty string and on a short document returned content from
the wrong region (e.g. lines 11-30 of a 30-line file in response to a
request for the head of the document). The lineNumbers branch was the
same shape: addLineNumbers(text, -19) emitted "-19:", "-18:" prefixes.

Same buggy slice lived in the CLI getDocument path independently.

Fix in three layers, plus the docstring:

- src/mcp/server.ts: clamp parsedFromLine to >= 1 after parsing input
  args and the :line suffix, before it reaches getDocumentBody and
  addLineNumbers. Also tighten the query tool's recommendation to
  `fromLine = max(1, line - 20)` so following the docstring literally
  produces a valid value.
- src/cli/qmd.ts: same clamp on the CLI getDocument fromLine after
  the colon-suffix parse.
- src/store.ts: defensive Math.max(0, ...) on the slice start in
  getDocumentBody so SDK callers and any future entry points are
  protected without relying on every caller remembering to clamp.
- test/store.test.ts: regression test on getDocumentBody with
  fromLine = -19 returns the head of the document, not the tail.
- test/cli.test.ts: regression test on `qmd get --from -19` matches
  the no-flag baseline (head of document).

src/cli/qmd.ts

@@ -844,6 +844,7 @@ function getDocument(filename: string, fromLine?: number, maxLines?: number, lin
       inputPath = inputPath.slice(0, -colonMatch[0].length);
     }
   }
+  if (fromLine !== undefined) fromLine = Math.max(1, fromLine);
 
   const parsedIndexPath = isVirtualPath(inputPath) ? parseVirtualPath(inputPath) : null;
   if (parsedIndexPath?.indexName) {

src/mcp/server.ts

@@ -243,7 +243,7 @@ async function createMcpServer(store: QMDStore): Promise<McpServer> {
       title: "Query",
       description: `Search the knowledge base using a query document — one or more typed sub-queries combined for best recall.
 
-Each result includes a \`line\` field with the absolute 1-indexed line of the best match in the source markdown. To read more context around a hit, call \`get(file, fromLine = line - 20, maxLines = 80, lineNumbers = true)\`.
+Each result includes a \`line\` field with the absolute 1-indexed line of the best match in the source markdown. To read more context around a hit, call \`get(file, fromLine = max(1, line - 20), maxLines = 80, lineNumbers = true)\`.
 
 ## Query Types
 
@@ -389,6 +389,7 @@ Intent-aware lex (C++ performance, not sports):
         parsedFromLine = parseInt(colonMatch[1], 10);
         lookup = lookup.slice(0, -colonMatch[0].length);
       }
+      if (parsedFromLine !== undefined) parsedFromLine = Math.max(1, parsedFromLine);
 
       const result = await store.get(lookup, { includeBody: false });
 

src/store.ts

@@ -3800,7 +3800,7 @@ export function getDocumentBody(db: Database, doc: DocumentResult | { filepath:
   let body = row.body;
   if (fromLine !== undefined || maxLines !== undefined) {
     const lines = body.split('\n');
-    const start = (fromLine || 1) - 1;
+    const start = Math.max(0, (fromLine || 1) - 1);
     const end = maxLines !== undefined ? start + maxLines : lines.length;
     body = lines.slice(start, end).join('\n');
   }

test/cli.test.ts

@@ -542,6 +542,13 @@ describe("CLI Get Command", () => {
     // Should indicate file not found
     expect(exitCode).toBe(1);
   });
+
+  test("clamps negative --from to top of file (no silent tail content)", async () => {
+    const baseline = await runQmd(["get", "README.md"]);
+    const negative = await runQmd(["get", "README.md", "--from", "-19"]);
+    expect(negative.exitCode).toBe(0);
+    expect(negative.stdout).toBe(baseline.stdout);
+  });
 });
 
 describe("CLI Multi-Get Command", () => {

test/store.test.ts

@@ -1713,6 +1713,21 @@ describe("Document Retrieval", () => {
       expect(body).toBeNull();
       await cleanupTestDb(store);
     });
+
+    test("getDocumentBody clamps negative fromLine to top of document", async () => {
+      const store = await createTestStore();
+      const collectionName = await createTestCollection({ pwd: "/path" });
+      await insertTestDocument(store.db, collectionName, {
+        name: "mydoc",
+        displayPath: "mydoc.md",
+        body: "Line 1\nLine 2\nLine 3\nLine 4\nLine 5",
+      });
+
+      const body = store.getDocumentBody({ filepath: "/path/mydoc.md" }, -19, 80);
+      expect(body).toBe("Line 1\nLine 2\nLine 3\nLine 4\nLine 5");
+
+      await cleanupTestDb(store);
+    });
   });
 
   describe("findDocuments (multi-get)", () => {