vahtian (Python)

Reproducible, provenance-first evidence tooling. Freeze a record set into a content-hashed, provenance-stamped, date-locked corpus; verify reproducibility; keep a hash-chained audit trail. Stdlib-only.

The same core and on-disk format exist in the R package vahtian, so a corpus frozen in Python verifies in R and vice versa.

import vahtian
corpus = vahtian.freeze(records, search_date="2026-06-23")
corpus.save("frozen-corpus")          # frozen-corpus.jsonl + .manifest.json
assert vahtian.verify(corpus)         # tamper-evident

L = vahtian.Ledger()
L.append("human:hha", "rate", {"record_id": "pmid:12345", "value": "supported"})
L.append("ai:opus/pv1", "advise", {"record_id": "pmid:12345", "value": "supported"})
assert L.verify()                     # retro-edits break the chain

Compare a claim against a cited source's finding, deterministically. An assistant (AI or human — the ledger records which) reduces each to the same structured Assertion; compare() is plain code that reports where the two agree, conflict, or say nothing, and proposes a candidate label. A human makes the decision — the comparator never does — and every step lands in the ledger. It checks claim–source support, not truth.

from dataclasses import asdict

claim  = vahtian.Assertion(outcome="all-cause mortality", direction="decrease",
                           effect_type="HR", effect_value=0.72,
                           quote="cut mortality (HR 0.72)")
source = vahtian.Assertion(outcome="all-cause mortality", direction="decrease",
                           effect_type="HR", effect_value=0.72, locator="table 2")

L.append("ai:opus/pv1", "extract_claim", asdict(claim))
L.append("ai:opus/pv1", "extract_source", asdict(source))
a = vahtian.compare(claim, source)    # deterministic; same inputs → same result
a.record(L)                           # candidate "aligned", hashes of both inputs
L.append("human:hha", "decide", {"decision": "supported",
                                 "candidate": a.candidate,
                                 "claim_hash": a.claim_hash})
assert L.verify()

A field carries not just a value but why it holds one. A plain value is taken as explicitly stated and None as not stated; the other states are marked so a single None never collapses them together:

vahtian.Assertion(
    direction=vahtian.inferred("decrease"),   # inferred, not explicitly stated
    comparator=vahtian.not_applicable(),      # doesn't apply to this design
    effect_value=vahtian.extraction_failed(), # extractor couldn't read it
    outcome=vahtian.ambiguous("mortality"),   # stated, but ambiguously
)

An inferred field never reaches an aligned candidate without a human confirming it, and an extraction failure stays distinct from source silence (it routes back to extraction).

Local MCP server

Expose the reproducibility core to an AI agent over MCP — running locally, on your machine, over stdio. Nothing is uploaded; the agent calls the same deterministic functions shown above. The agent proposes and records; the human decides.

pip install "vahtian[mcp]"
vahtian-mcp            # runs the stdio MCP server

Connect it to an MCP client. Claude Code:

claude mcp add vahtian -- vahtian-mcp

Claude Desktop (claude_desktop_config.json):

{ "mcpServers": { "vahtian": { "command": "vahtian-mcp" } } }

Tools (all local, deterministic, no network):

The server checks reproducibility and records who did what; it does not judge evidence or establish truth.

vahti (Finnish) = sentinel / guard. Human-first. AI-second. Auditable. Apache-2.0.