Module target_defaults 

Resolving the compiled target’s serving defaults — baked first, environment second.

The defect this closes

Maintainer review of the H100 integration branch, 2026-09-11 (tbraun96):

There is no arch separation at all. H100 builds compile GB10’s kernel tree. Every Hopper/GB10 divergence is expressed as an env lever set by an H100 recipe living outside this repo — not as arch-selected code. “No interference” rests on discipline rather than structure.

Every lever here used to read the environment and fall back to a literal that described GB10. The H100 configuration therefore lived in a launch script nobody in this repository could see, review or test, and “GB10 is unaffected” was a promise about which prefixes people remembered to type.

Now the fallback is atlas_kernels::TARGET_DEFAULTS, baked by build.rs from the ONE kernels/<hw>/HARDWARE.toml this binary compiled ([defaults]). A GB10 build cannot carry Hopper’s numbers, an H100 serve needs no prefixes, and every value is reviewable beside the arch it belongs to.

The override grammar

input	meaning
variable absent	the baked target default
0, false, off, no (any case, trimmed)	OFF — explicit override
any other value, including empty	ON — explicit override

⚠️ VAR=0 NOW MEANS OFF. These levers were PRESENCE-gated (var_os(..).is_some()), chosen so an A/B recipe could stay a bare VAR=1 prefix with no “=0 means on” trap. Presence cannot express “off”, and once a target’s default can be ON, an operator with no way to turn a lever off is back to editing launch scripts. The trap the old rule avoided is gone in the direction that matters: VAR=0 now means what it reads as. VAR=1 is unchanged everywhere.

The legacy ATLAS_NO_* kill switches stay PRESENCE-gated and still force their lever OFF, so no script that predates this file changes meaning. ATLAS_NO_DECODE_SPLIT_SILU is the one in this table.

One resolution, one log line

resolved is the SSOT: every consumer below reads it, and spark-server prints it as target defaults (<hw>): … with the environment-sourced values marked. A lever resolved in two places is a lever that can disagree with the line that claims to report it.

Adding a lever — the contract

ONE commit touches all of: the field in atlas_kernels::TargetDefaults, the parse arm in atlas-kernels/build_defaults.rs, the row in EVERY kernels/<hw>/HARDWARE.toml that has a [defaults] table, the TargetLevers field and its arm in resolve, the field in format_levers’s line, and a test. parse_defaults panics on an unknown key, so a half-landed lever fails the build rather than reading as agreement with the baseline.

★ And the commit that does all that is the one landing the lever’s CONSUMER. A row whose dispatch site does not exist yet cannot be graded, answers nothing when an operator sets its variable, and puts an (env) tag in the boot line against a decision that changes no code. So a kernel PR brings its own row; this module ships only the rows whose arms are already here.

Structs

Resolved

A resolved lever and where it came from.

TargetLevers

Every serving lever this target declares, resolved against the environment.

Enums

Source

Where a resolved value came from — the whole point of the log line.

Constants

BASELINE_BATCHM_MAX

The declaration a target that says nothing gets — kept in sync with atlas-kernels/build_defaults.rs::baseline by target_defaults_tests::the_baseline_band_is_the_frozen_one.

Functions

declared

The baked declaration this binary carries, for the serve log’s header and for callers that must stay pure over their own inputs (ModelLevers).

format_levers

summary_line over a table the caller already has — pure, so the line can be graded for ANY target from a CPU test without touching the process environment or sealing the OnceLock.

resolve

The whole table, as a pure function of the baked declaration and a variable lookup — so the resolution is testable for ANY target from a CPU test, on any host, without touching the process environment.

resolve_batchm_max

The BF16 decode head’s batched-GEMV band.

resolve_max_m

Upper M for the W8A8 dense-FFN prefill, per projection shape.

resolve_toggle

The override grammar for a boolean lever, as a pure function.

resolved

The process-wide resolution.

summary_line

target defaults (<hw>): … — one line naming every resolved value and which came from the environment.