feat(serve): load taxonomy packages and page long networks

[jfrench9]

Summary

load_filing refused a taxonomy published on its own (a zip of schemas and linkbases with no report), even though every tool reads its DTS once Arelle is pointed at the right schema. A package with no report now loads from an entry point, by path or by URL. Once loaded, a taxonomy's networks outran the 400-row cap with no way to reach the rest, so statement and information_block now page.

Taxonomy support is a load format, not a new lane: no new tools, one optional parameter on load_filing, and reports load exactly as before.

Changes

serve/session.py (loading)

• A zip or directory with no inline document or instance loads from an entry point: the first one META-INF/taxonomyPackage.xml lists, resolved into the package through its catalog's rewriteURI; or, with no manifest, the one schema nothing else in the package imports. With no manifest and several root schemas, the load asks for one.
• FilingSession.load takes entry_point to load another, matched by path in the package, file name, stem or manifest name. An ambiguous or unknown name is refused with the candidates listed. entry_point on a source that is not a package is refused.
• An elements-only entry point (no linkbases, so no networks for the model to reach) is refused as such, naming the entry points that have networks, instead of "not XBRL".
• A .zip URL is downloaded and loaded as a local package. This is also the path a report zip given by URL now takes, the same one lei: / filings.xbrl.org loads already use.
• _find_load_target returns None instead of raising when a package holds no report.

serve/tools.py (surface)

• The load receipt and describe_filing carry a taxonomy block: the entry point loaded and the others on offer. The next steps for a taxonomy point at resolve_element, disclosures, statement and information_block.
• statement and information_block take offset. A truncated response returns next_offset; the pages join into the unpaged rows with depths intact. A later page carries ancestors (the headers above its first row). information_block returns axes, calculation and text with the first page only. An offset past the end is refused with the row count.

serve/server.py + serve/README.md

• MCP: entry_point on load_filing, offset on statement and information_block. The tool text grows by one sentence each, since it ships in every client's prompt; the detail lives in serve/README.md.

Output Impact

BROADER COVERAGE: taxonomy packages that previously failed to load now load (FASB US GAAP / SRT, and manifest-less packages such as GASB's 2026 taxonomy exposure draft). Holon, TAVI and model output are unchanged; serialize/ is untouched.

MCP surface changes are additive: new optional parameters and a taxonomy key present only on taxonomy loads. The CLI is unchanged; xbrlkit serve / view take a taxonomy zip as a source but have no --entry-point flag. The robosystems information-block operation calls information_block with keyword arguments, so the new offset parameter does not affect it.

Testing

just test-all (via the commit hook): ruff, format, basedpyright clean; 544 passed, 2 skipped.

New tests (hermetic, Arelle mocked at _parse): root-schema detection that ignores linkbase back-references, several roots asking for one, manifest order with a catalog-rewritten URL and a relative href, entry-point matching and its errors, the receipt block, the elements-only refusal, a zip by URL, entry_point refused off-package, and paging that joins back into the unpaged rows for both tools.

Real loads through the branch code (no report, so no accession numbers):

Source	Entry point chosen	Concepts	Networks (pre / cal / def)
gasb-exposure-2026.zip (no manifest)	gasb-exposure-2026.xsd	855	147 / 0 / 735
us-gaap-2025.zip	entire/us-gaap-entryPoint-all-2025.xsd, 10 others listed	20,699	118 / 65 / 2,414
us-gaap-2025.zip, entry_point="us-gaap-entryPoint-std-2025"	entire/us-gaap-entryPoint-std-2025.xsd	18,232	111 / 65 / 2,372
https://xbrl.fasb.org/us-gaap/2026/us-gaap-2026.zip	entire/us-gaap-entryPoint-all-2026.xsd	20,617	117 / 65 / 2,353
https://xbrl.fasb.org/srt/2026/srt-2026.zip	entire/srt-entryPoint-all-2026.xsd	3,578	22 / 2 / 203

US GAAP 2025 network counts were checked against the raw linkbases the entry point reaches: 111 FASB presentation roles (+7 from the SEC taxonomies it imports), 65 calculation roles, 397 FASB definition roles (+11 SEC). The classified balance sheet pages to 691 rows over two calls; Liabilities, StockholdersEquity and LiabilitiesAndStockholdersEquity, previously unreachable past the cap, sit at rows 535, 594 and 690. The Leases (Topic 842) block pages to 771 rows over two calls.

Known and left alone: resolve_element ranking has no fact counts to lean on in a taxonomy ("revenue" on US GAAP does not rank us-gaap:Revenues first), and GASB's statements are not classified as statements. Both wait for real demand.