A token budget is an API contract

• claim · 01Shipped

  A hard ceiling of 500 tokens

  The builder aims for 400 and hard-fails nothing: it walks a fixed reduction ladder, dropping the least valuable content first, and then clamps every remaining optional field if the document still does not fit. The ceiling is a constant, and the test suite asserts it against adversarial events with 500 frames and 500 breadcrumbs.
• claim · 02Shipped

  The count is published, and rounds against us

  Every essence carries its own estimatedTokens. The estimator is a deliberate heuristic — characters divided by 3.6 — rather than a BPE tokenizer, because it must run on every event in the pipeline without a native dependency. At 3.6 characters per token it sits below the usual estimate for English-plus-code, so an agent that trusts the published number is never surprised by a bigger document than advertised.
• claim · 03Shipped

  What was dropped is reported back

  Truncation is not silent. A hidden frame count names how many frames were omitted, and each hydration handle carries a reason that distinguishes “there is no more stack” from “the rest of the stack costs 900 tokens.” The agent decides whether to pay for the rest.
• claim · 04Shipped

  Every attacker-controlled string is labelled

  Error messages are attacker-controlled input, and in June 2026 prompt injection via a fabricated error report into a repo-write coding agent stopped being hypothetical. So every string carries a trust label — platform, repository, untrusted, or quarantined — and a quarantined value is replaced before it is served. The MCP server exposes no argument that un-redacts it; the opt-in does not exist to be found.
• claim · 05Shipped

  The format is published, not proprietary

  The essence is specified as a standalone format any vendor could implement, with a JSON Schema generated from the same schema the server uses — so the two cannot drift — plus worked examples, a versioning policy and a conformance checklist. The schema version is on every document, and you can pin it.
• claim · 06Shipped

  The budget is a serving concern, not a capture concern

  The SDK captures rich and bounded; the compression happens server-side. Context not captured at event time is gone forever, and fix quality is capped by capture breadth — so the essence is a projection that can improve without anyone shipping an SDK release.

The essence contract documents the budget, the reduction ladder and the trust labels as they are built. The published specification is what the format is, with a conformance checklist and a versioning policy.