fix: reject orphan positional inline bodies in generic decoder (SPEC 16.5)

The object-body parser silently skipped any line it did not recognize as a
section, a key=value field, or an inline array. A stray positional inline body
(a pipe-delimited line with no eligible ^{} cell, e.g. a 2nd 'Bob|b@t.com' after
a row's one inline cell was filled) fell through once the row count was satisfied
and was DROPPED with no error - silent data loss, a lossless round-trip hole.
Such lines are now rejected: a pipe-delimited line as orphan_inline_attachment,
any other unrecognized line as invalid_line. Verified that no legitimate encoder
output reaches this catch-all (full conformance + property round-trip + fuzz green;
legitimate root fields after a nested ## section still decode).

Author: blackwell-systems

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixes
 
 - Decoder: reject an orphan `.field` attachment (a `.field` whose name is neither a `^`-marked column of its row nor a `>`-containing field name, SPEC 7.4.6.1.4) instead of silently absorbing it as an undeclared extra field. Such a stray attachment previously decoded to a record no encoder produces, silently injecting a field onto the last-parsed row (a lossless round-trip hole); now rejected per SPEC 16.5 (`orphan_attachment`).
+- Decoder: reject an orphan positional inline body (a pipe-delimited line with no eligible `^{}` attachment-marker cell) instead of silently dropping it. The object-body parser previously skipped any unrecognized line, so a stray positional body (e.g. a second `Bob|b@t.com` after a row's one inline cell was filled) vanished with no error (silent data loss); now rejected per SPEC 16.5 (`orphan_inline_attachment`).
 - Graph streaming trailer: the edge count is now always the last `counts` entry, even when the stream has no edges (positional `counts=2,1,0`; labeled `counts=…,edges:0`). A zero-edge stream previously dropped it, violating the SPEC §8.4 / §8.4.1 rule that the edge count is always present and last (the invariant that keeps the positional form unambiguous). The graph trailer is decoder-ignored, so this changes producer output only.
 
 ### Streaming: opt-in labeled trailer counts (SPEC §8.4.1)

src/gcf/decode_generic.py

@@ -177,7 +177,14 @@ def _parse_object_body(
                         i += 1
                         continue
 
-        i += 1
+        # An object-body line that is not a `## ` section, a `key=value` field, or
+        # an inline array is not valid content and MUST NOT be silently skipped
+        # (that dropped data, a lossless round-trip hole). A pipe-delimited line is
+        # a stray positional inline body with no eligible `^` cell (SPEC 16.5,
+        # orphan_inline_attachment); any other unrecognized line is likewise rejected.
+        if "|" in content:
+            raise ValueError(f"orphan_inline_attachment: {content}")
+        raise ValueError(f"invalid_line: unexpected content in object body: {content!r}")
     return i - start