fix: adversarial review fixes (GST-620)

A field may count as both a label and an identifier (a pushed label_keys can no longer hide a join); TSV cells may be quoted; a file that never names a label key is skipped before parsing; blobs are parsed as they are read; label_join refusals no longer suggest allow_paths.

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

docs/pregate.md

@@ -999,7 +999,7 @@ gstack-pregate sealed [--range <a..b>] [--remote origin] [--base <branch>] [--js
   `plan_bytes` tells a model under test which unit it is. A record is a JSON
   object at any depth (its own fields plus one level of nested objects, named
   like `meta.head`), a JSONL or NDJSON line, a CSV or TSV row, or a row of a
-  Markdown pipe table. Field names and table headers are compared after
+  Markdown pipe table (CSV and TSV cells may be quoted). Field names and table headers are compared after
   trimming, lowercasing and turning spaces and hyphens into underscores
   (`Tree SHA-256` is `tree_sha_256`); this is the rule's own normalization,
   separate from `case_insensitive`. An identifier is a field whose name
@@ -1010,7 +1010,9 @@ gstack-pregate sealed [--range <a..b>] [--remote origin] [--base <branch>] [--js
   to 64 hex characters with at least one digit and one letter a to f. An
   object key of that shape counts as an identifier of the object it holds
   (shown as `(key)`), so a map keyed by sha joins too. Numbers count only
-  through the field name. Both lists take bare field names: a nested field
+  through the field name. A field can be both a label and an identifier, and
+  a record joins when it has a label field and a different identifier field,
+  so adding identifier names to `label_keys` never hides a join. Both lists take bare field names: a nested field
   matches by its own name (`stratum`, never `meta.stratum`). For each supported file a commit adds,
   modifies, renames or copies, the guard fingerprints every joined record
   (sha256 over its label and identifier fields and their values, kept in
@@ -1018,7 +1020,9 @@ gstack-pregate sealed [--range <a..b>] [--remote origin] [--base <branch>] [--js
   rename or copy source; every parent for a merge). A fingerprint no parent
   has is a finding, so unchanged records and formatting-only edits stay clear,
   and a replaced, added or widened record refuses even when the count stays
-  the same. A supported file over 4 MiB, one that does not parse (one bad
+  the same. A file whose text never names a label key cannot hold a join, so
+  it is skipped without parsing (a commented `tsconfig.json` passes). A
+  supported file over 4 MiB, one that names a label key and does not parse (one bad
   JSONL line is enough), one nested deeper than 64 levels, or a blob git
   cannot read is `sealed.label_join_unchecked`. It refuses too, and the
   `SEALED:` line counts it as `unchecked=<n>`. Findings print field names

docs/troubleshooting.md

@@ -3905,8 +3905,8 @@ it). A publishable file kept next to sealed data (a `MANIFEST.json` of hashes
 and counts) can be exempted from the path rules with a `sealed.allow_paths`
 glob in the base branch's `.gstack/pregate.json`; the text rules still read it
 ([docs/pregate.md#sealed](pregate.md#sealed)). For `sealed.label_join`, drop
-the identifier fields (or the labels) from the published file, or move it under
-a sealed path; `allow_paths` never exempt it. A reviewed false positive gets
+the identifier fields (or the labels) from the published file, or keep the file
+out of the public repository; `allow_paths` never exempt it. A reviewed false positive gets
 one line in the base branch's
 `.gstack/sealed-allow.tsv`: `rule<TAB>path<TAB>sha<TAB>reason`, where `sha` is
 the full commit sha (a shortened one is ignored and named on stderr). A private