Audience is expressed by placement, never by a prose register

Context

The repository has always behaved as if audience is a property of where text lives, not how it is written: the three-tier layout keeps the agent-heavy development record apart from user-facing docs/; the "JSON internal, MD render" invariant assigns machine consumers to machine surfaces (--json payloads, the generated CLI reference); and the rules loader injects agent guidance as data, not as documentation prose. But no record ratified that position, and on 2026-08-28 the question became live: a proposal to extend the writing-style guide with a two-register audience model — product prose written for humans, technical prose assumed to be consumed mostly by AI agents.

The prefer-sota sequence ran in full: an independent fit-challenge over the repo's record, then an independent SOTA research pass, recorded in the dated research note 2026-08-28-docs-audience-style-sota. Both converged. The field's evidence is that well-structured human documentation serves agents as-is, that the adopted split is by artifact class (docs for everyone; dedicated instruction files for agents), and that the strongest dedicated-machine-surface experiment (llms.txt) failed on adoption data. The fit-challenge found a register axis would duplicate the placement boundary the tier layout already owns, and would open a per-page "agent-register" exemption no path-scoped lint rule can see.

Decision

Audience is expressed by placement and machine surfaces, never by a prose register:

1. docs/ is written for human readers, in one register. There are no parallel agent-facing versions of documentation pages.
2. The machine audience is served by machine surfaces: --json payloads, the generated CLI reference, the AGENTS.md router, and the rules loader. When a page seems to need an agent-specific rendering, the remedy is a machine surface, not restyled prose.
3. A page's density is set by its Diátaxis type, not by an audience guess. A page too dense for its reader is mis-typed or mis-placed, never re-registered.
4. No rule in the writing-style guide may be conditioned on a page's supposed audience; the guide binds docs/ and README.md uniformly.

Alternatives Considered

1. Two prose registers inside docs/. Rejected: it bifurcates maintenance, contradicts the docs/ charter ("user-facing only"), has no SOTA support, and silently weakens every path-scoped machine-enforced rule by inviting register-based exemptions.
2. A dedicated machine-readable docs surface (llms.txt class). Rejected on adoption evidence (~10% adoption, ~97% zero traffic, no provider commitment). Revisit only if a major consumer commits to reading it; the repo's own consumers already read AGENTS.md and the rules loader.
3. Keep the position unratified. Rejected: the question recurs (recurrence-is-signal), and an unrecorded position invites relitigating it page by page.

Consequences

The writing-style guide gains an Audience section citing this ADR, so the reference page describes a ratified fact rather than an assumption. Future "write this for agents" requests route to machine surfaces. Reversing this position is a new ADR that supersedes this one.