SeenRelay Python client

Measure and avoid redundant expensive validation.

Deterministic, standard-library-only client that places SeenRelay CHECK around repeated source-backed validation while preserving the application's original validation by default.

Version 0.2.1 is behavior-equivalent to 0.2.0; it refreshes package discovery metadata and documentation. Python remains conservative and shadow-first by default. The local-first Zero-State, generic dispatcher and MCP interception modules are JavaScript / TypeScript features; Python parity is not claimed.

Install

pip install seenrelay==0.2.1

Smallest integration: bind once, one line per revalidation

from seenrelay import SeenRelayClient
from seenrelay_easy import protect_validation

relay = SeenRelayClient()

validate_price = protect_validation(
    relay,
    fact=fact,
    validate=lambda ctx: expensive_validation(ctx.conditional_headers),
)

value = validate_price(known_value)

That is strict shadow mode by default: SeenRelay CHECK runs, your original validation still runs, and the independently obtained result is OBSERVEd best-effort. Nothing is skipped merely because SeenRelay is installed.

Only after measurement and policy approval should you add an explicit reuse policy:

from seenrelay import reuse_known_on_same_observed

validate_price = protect_validation(
    relay,
    fact=fact,
    validate=lambda ctx: expensive_validation(ctx.conditional_headers),
    reuse=reuse_known_on_same_observed,
)

Direct client form

value = relay.guard(
    fact=fact,
    known_value=known_value,
    validate=lambda ctx: expensive_validation(ctx.conditional_headers),
)

Without an explicit reuse policy, validation is never skipped.

Prove value before enabling reuse

from seenrelay import SeenRelayClient
from seenrelay_shadow import SeenRelayShadowProof

proof = SeenRelayShadowProof(SeenRelayClient())

value = proof.guard(
    fact=fact,
    known_value=known_value,
    validate=lambda ctx: expensive_validation(ctx.conditional_headers),
)

print(proof.report(
    avoided_validation_cost=0.01,
))

Shadow Proof always keeps the original validation. It measures CHECK status distribution, validation time and SeenRelay request latency locally. Potential savings count only SAME_OBSERVED calls and subtract caller-supplied request costs. Savings from conditional ETag / Last-Modified requests are deliberately excluded unless measured separately by the application.

Use SeenRelay around repeated validation that is materially more expensive than the preflight: paid search, scraping/proxy work, browser or extraction calls, rate-limited APIs, model-assisted parsing, or multi-step validation. It is generally a poor fit for a cheap one-off GET.

Protocol boundary

The Python client does not add a SeenRelay operation. The hosted service still exposes only CHECK and OBSERVE and does not browse, search or verify arbitrary facts on demand.

License

The client package is MIT licensed. The hosted SeenRelay service implementation remains governed by the repository root license.