Module kernel 

The kernel’s boundary, and the five seams through which everything else enters (KERNEL.1, 2026-10-06; the design is web/CALLOSUM.md §14).

The kernel holds mechanism only: forms and their expansion, the emitters, the sheet model, recalculation over a declared subset once it lands, the relation set, and the ABI. It never holds English, message text, a default, chrome, a format beyond a trait, or a door. Each of those is data the kernel reads (the four tables under core/data/, a phrasebook, a library) or an implementation of one of the seams below. The rule that follows: the kernel grows a seam, never a feature.

tools/check_kernel_boundary.ps1 pins the rule over core/src/. This module writes the seams down as data, so that a test can hold their counts and frazaro describe (KERNEL.18) can print them, and names the two traits whose first implementations later items land: Engine (PORT.9) and Projection (KERNEL.4).

Structs

Format

A file format the kernel reads, writes, or both.

HostProfile

A door’s host profile: the statement heads it carries out with nothing running, and the catalogue id that refuses the rest by name.

Seam

One of the five entrances into the kernel.

Window

A window onto the model: one sheet by name, one rectangle of it.

Constants

FILE_DOOR

The file door: frazaro build, and the page’s Workbook strip. What the walker in build.rs holds, read off its arms: a value or a formula into a range, Work on sheet and Go to sheet, a condition that folds, and a call of one of the program’s own steps with no values, inlined. The rest is refused with the sentence quoted.

FORMATS

The formats seam’s registry. reflect::open picks the reader by the bytes it is handed; the one writer is sheet::ooxml::workbook_bytes.

HOST_PROFILES

The host profiles the kernel knows. The Excel add-in needs none, since it holds every form; the page’s viewport and the task pane add theirs with KERNEL.19.

SEAMS

The five seams, in the order CONTRIBUTING.md lists them.

Traits

Engine

An engine: tables in, a table out, under a symbol of the head table, held by proof files of one kind. The relation type is the implementor’s, since the port of VLA_Relation (PORT.9) defines it; the first implementations are SQL, DATALOG, PROLOG and OPTIMIZE, and a fifth proves the seam takes additions.

Projection

A projection: a pure function from the model and a window to lines, the shape every door prints (SD-23). The grid is the first (KERNEL.4), the sentence pane the second, the dependency cone drawn as a diagram the third (KERNEL.12). A projection never edits the model.

Functions

seams

The seams, as data.