Add arguman-legal external connector (Turkish/ECtHR/BGH multilingual case-law research)

[argumanai]

Summary

Adds arguman-legal, a partner-built MCP connector for Turkish, European, and German case-law research, to external_plugins/. First Turkish-jurisdiction plugin in the directory and the first multilingual cross-lingual search plugin (Turkish queries surface English/French ECtHR judgments and German BGH rulings in their original languages).

What's included

• external_plugins/arguman-legal/
  • .claude-plugin/plugin.json — plugin manifest (arguman.ai, v0.1.0)
  • .mcp.json — HTTP MCP endpoint with OAuth 2.1 (PKCE + Dynamic Client Registration)
  • skills/caselaw-search/SKILL.md — multilingual case-law search workflow (collection mapping, doctrinal Turkish translation, drift detection)
  • skills/citation-network/SKILL.md — anchor → similar → citing-cases lineage traversal
  • skills/karsi-arguman/SKILL.md — counter-argument finder for litigation prep (5-level threat classification)
  • README.md — vendor docs (When to Use / Not / Examples / Known limitations / Links)
• .claude-plugin/marketplace.json — registers arguman-legal, appended to the array per the I1 curated-order note
• README.md — adds layout entry, "External / partner-built" table row, MCP Connectors table row, and a skill-listing section (matching the cocounsel-legal pattern)

What this fills

First Turkish-jurisdiction plugin in the directory. Partially closes #25 (jurisdiction-specific support) for Türkiye specifically.

Coverage spans the courts whose rulings shape Turkish law in practice — Yargıtay (Court of Cassation), Danıştay (Council of State), Anayasa Mahkemesi (Constitutional Court — norm review + individual application), Uyuşmazlık Mahkemesi (Conflicts Court) — plus the full multilingual HUDOC corpus of ECtHR and the German Bundesgerichtshof (criminal and civil). Nearly 15 million rulings indexed across 8 collections.

The cross-lingual differentiator: A Turkish lawyer researching Article 8 ECHR jurisprudence can query in Turkish ("özel hayata saygı — telefon dinleme") and the embeddings will surface relevant English/French Strasbourg judgments. Same for Turkish-to-German BGH comparative work (essential for academic and doctoral research, since Turkish private law and criminal law doctrine borrow heavily from the German tradition).

Connector quality vs. CONNECTORS.md criteria

Criterion	This plugin
Remote MCP over HTTPS	✓ Cloud Run, europe-west3
OAuth or API-key auth	✓ OAuth 2.1 with Dynamic Client Registration (RFC 7591) + PKCE — no static client ID, no manual API key issuance
Read-heavy tools	✓ All 5 tools are read-only: case_lookup, get_full_text, find_similar, search, infaz_hesaplama (pure calculation, no side effects)
Provenance in results	✓ Each hit returns esas no + karar no + tarih + daire + collection ID + point_id (or Application No. / Beschwerde-Nr. for ECtHR/BGH)
No instruction-like content	✓ Tool descriptions tag metadata explicitly; results returned as structured JSON; no string-embedded instructions
Graceful errors	✓ HTTP 429 with Retry-After, structured {error: {code, message}} envelope
Discovery metadata	✓ .well-known/oauth-protected-resource and .well-known/oauth-authorization-server endpoints live and serving correctly

Test prompts a reviewer can run

After installing the plugin and authorizing via the OAuth flow:

1. Turkish case-law search:
   "Cezada haksız tahrik indirimi — son Yargıtay 1. CD içtihatları"
   → triggers caselaw-search skill, runs search on ceza collection
2. Cross-lingual ECtHR research:
   "Türkiye'deki gazetecilere yönelik ifade özgürlüğü ihlalleri — AİHM kararları"
   → triggers caselaw-search on aihm collection, surfaces EN/FR judgments via cross-lingual embeddings
3. Citation network:
   "Esas 2023/14587 numaralı Yargıtay 1. CD kararının tam metnini getir, sonra bu karara atıf yapan diğer kararları listele"
   → case_lookup → get_full_text → find_citing_cases
4. Counter-argument:
   "Müvekkilim haksız tahrik indirimi alacak. Karşı tarafın itiraz edebileceği Yargıtay kararları nelerdir?"
   → triggers karsi-arguman skill — negation search + element-attack search + threat classification
5. Turkish criminal infaz calculation:
   "5275 sayılı Kanun kapsamında 8 yıl hapis cezası, sabıkasız, tek suç için infaz süresini hesapla"
   → infaz_hesaplama tool

Companion documentation (public)

• MCP catalog: https://arguman.ai/docs/mcp/en
• OAuth flow: https://arguman.ai/docs/mcp/en/auth
• Data coverage: https://arguman.ai/docs/mcp/en/coverage
• Privacy: https://arguman.ai/privacy
• Terms: https://arguman.ai/terms
• MCP endpoint: https://arguman-mcp-915822535803.europe-west3.run.app/mcp
• Health probe: https://arguman-mcp-915822535803.europe-west3.run.app/health
• OAuth metadata: https://arguman-mcp-915822535803.europe-west3.run.app/.well-known/oauth-authorization-server

Known limitations (transparent disclosure)

• AYM bireysel başvuru coverage starts from late 2012 (when the individual application procedure became operative); pre-2012 individual applications are not indexed. Earlier norm-control AYM decisions are covered.
• BGH coverage is concentrated post-1990; older Bundesgerichtshof rulings are sparse.
• HUDOC TR translations of ECtHR judgments are not separately indexed — the index uses the original-language corpus (primarily EN/FR) with cross-lingual semantic retrieval. Users needing verbatim Turkish text of an ECtHR judgment should use the official European Court translation services after locating the case here.
• Reverse-citation graph traversal at scale is not yet exposed. find_citing_cases operates one hop at a time. Planned for a future release.

Notes for review

• The marketplace.json array uses a curated display order per the I1 note in root CLAUDE.md; I appended at the end. Happy to re-sort if you prefer.
• Auth: this MCP uses Dynamic Client Registration, so unlike cocounsel-legal/.mcp.json no static clientId is shipped — the Claude client registers itself per install.
• Skill frontmatter uses the bare name: <skill> form (matching first-party convention) rather than the <plugin>:<skill> form CoCounsel chose; both resolve correctly in the slash-command runtime.
• All 5 tools include title and readOnlyHint: true annotations.
• Tested with claude plugin validate external_plugins/arguman-legal/ — passes clean.
• No plugin-level CLAUDE.md is shipped (consistent with the vendor pattern: external plugins are vendor-maintained, the first-party CLAUDE.md convention is for repo-internal plugins).

How this fits alongside existing plugins

• litigation-legal users practicing in Turkey or representing Turkish parties in international forums → case-law research and counter-argument layer
• regulatory-legal users working on Turkish regulatory matters → AYM constitutional review jurisprudence
• ip-legal users doing comparative patent/trademark analysis → BGH precedents (German doctrine is the primary comparative anchor for civil-law IP regimes)
• Academic and doctoral researchers at Turkish law faculties → cross-lingual TR ↔ ECtHR ↔ BGH analysis in a single query

CLA

Will sign on PR open via the CLA Assistant bot comment.

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[github-actions]

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[argumanai]

I have read the CLA Document and I hereby sign the CLA

[argumanai]

URL update notice 📝

We've just added a branded URL — the connector is now available at:

🔗 https://mcp.arguman.ai/mcp (preferred)

Latest commit (f73d3ca) updates .mcp.json and README.md accordingly.

The original Cloud Run URL (https://arguman-mcp-915822535803.europe-west3.run.app/mcp) remains active as a fallback — both addresses serve the same backend, so any reviewer or existing client testing with the old URL continues to work without disruption. OAuth metadata (/.well-known/oauth-authorization-server) now advertises mcp.arguman.ai as the canonical issuer regardless of which URL is hit.

No behavioral changes; just a cleaner address for the public listing.