2 files changed, 28 insertions(+), 2 deletions(-)

M mcpsrv/browse.go
M mcpsrv/browse_test.go

@@ 528,7 528,16 @@ func (s *Server) getCommitLog(ctx context.Context, in getCommitLogInput) (getCom
 		// ErrRefNotFound the same as any other ref it cannot resolve, and refMiss
 		// reads that sentinel here. A genuine failure of the store still takes the
 		// protocol arm below.
-		return out, refMiss(err, tool, noSuchRef(in.databaseRef, ref))
+		//
+		// The sentence names whichever of ref and from the call actually supplied:
+		// with a cursor set, ref is "" (it was never resolved, see above), and a
+		// refusal that named it anyway would send the caller looking for a typo in
+		// a branch name it never typed.
+		missing := noSuchRef(in.databaseRef, ref)
+		if from != "" {
+			missing = noSuchCursor(in.databaseRef, from)
+		}
+		return out, refMiss(err, tool, missing)
 	}
 
 	out.Ref = ref


@@ 743,6 752,14 @@ func noSuchRef(ref databaseRef, named string) string {
 	return fmt.Sprintf("%s has no branch or commit %q; list_branches names its branches", ref, named)
 }
 
+// noSuchCursor is get_commit_log's miss for a from-cursor that names no commit:
+// the counterpart of noSuchRef for the one call where a page can be continued by
+// hash instead of by ref, so the refusal points at "from" rather than sending the
+// caller to list_branches over a value that was never a branch name.
+func noSuchCursor(ref databaseRef, from string) string {
+	return fmt.Sprintf("%s has no commit %q to continue from; from takes the \"next\" hash a previous page of get_commit_log returned", ref, from)
+}
+
 func noSuchTable(ref databaseRef, at, table string) string {
 	return fmt.Sprintf("%s has no table %q at %q; list_tables names the tables there", ref, table, at)
 }

@@ 500,11 500,20 @@ func TestGetCommitLogWithABadCursorIsAMiss(t *testing.T) {
 		t.Run(from, func(t *testing.T) {
 			res := call(t, anonSession(t), "get_commit_log", args("notes", "from", from))
 			require.True(t, res.IsError, "a bad cursor is a tool result, not a protocol error")
-			assert.NotContains(t, errorText(res), "no database", "this is not the masked not-found")
+
+			text := errorText(res)
+			assert.NotContains(t, text, "no database", "this is not the masked not-found")
+			assert.Contains(t, text, from, "the refusal names the cursor the caller actually sent")
+			assert.Contains(t, text, "~alice/notes")
 		})
 	}
 }
 
+// TestAnUnresolvableRefIsAnAnswerAboutTheDatabase (above) already pins the other
+// half of this: a call that names a ref rather than a cursor gets a refusal
+// naming *that* ref. This test exists so the two halves are asserted in the same
+// place a reader looking for "does the cursor case name the cursor" would look.
+
 // --- the visibility matrix --------------------------------------------------
 
 // browseTarget is one fixture database with arguments valid for it, so that the