booth/docs/contracts/u7_navigation.contract.md

contract_version, status, module, purpose, depends_on, language, complexity, estimated_loc, confidence, used_by, touches, assumptions, open_questions

contract_version	status	module	purpose	depends_on	language	complexity	estimated_loc	confidence	used_by	touches	assumptions	open_questions
0.1-PROPOSED	PARTIALLY LANDED. The three components ROADMAP already ratifies — rail, filters, grid keyboard — are implemented and deployed (tests/test_navigation.py, 12 tests). The FOURTH, replacing directory sections with filename-derived groups, is NOT built and is the one scope-direction call below. The scope below departs from ROADMAP's U7 row on measured grounds and the operator has not ruled on it. Do not implement, and do not treat this as settled, until he has.	booth.items + booth.app (gallery navigation)	The last unit before the 1.0 cut. A gallery booth renders as one flat wall with no way to filter it, no way to move through it from the keyboard, and no grouping — so a review of sixty-odd renders is a scroll-and-squint. ROADMAP names four components: sections, a sticky rail, filters, grid keyboard. THE MEASUREMENT KILLS THE FIRST AND REPLACES IT: not one of the eleven live gallery booths has a subdirectory, so sections buy nothing, while a filename-prefix heuristic yields 5-16 sensible groups on four of the five large galleries. This unit ships the rail, the filters, the grid keyboard, and GROUPS DERIVED FROM FILENAMES rather than from a directory tree that does not exist.	booth.items.booth_items (INV-1: one resolver for item facts. `Item` gains ONE field, `group`, derived here and nowhere else. No route body derives it, exactly as no route body derives `section`, `caption` or `blurred`.) booth.items.Item.section (ALREADY EXISTS from U1 and STAYS. This unit does not delete it and does not render a rail from it — those are different questions. A booth that does have subdirectories keeps its section values; nothing regresses.) booth.app.build_gallery (the thin adapter over `booth_items`; it shapes items for the template and is where `group` reaches the page) booth.app.image_chain (the zoom prev/next ring. UNCHANGED, and named here because it was CHECKED: the ring is the item order filtered to images, and grouping must not reorder it -- a filter that changed what `next` means would misfile the operator's judgment, which is CLAUDE.md invariant 6's whole reason for existing.)	python + jinja + a little javascript	medium	300	0.6	booth.app.booth_view (the gallery page gains a rail and a filter state; the grid gains keyboard focus)	booth/items.py (the `group` field and its derivation) booth/app.py (build_gallery carries `group`; booth_view passes group counts) booth/templates/booth.html (the rail, the filter controls, the grid's focus affordances) booth/templates/base.html (rail + focus CSS) booth/static/embed.js (NOT TOUCHED — named because it was checked; the verbatim path has no grid) tests/test_items.py (group derivation) tests/test_navigation.py (new — rail, filters, keyboard) ROADMAP.md (the deterministic-order table gains the group row; U7's row is rewritten)	⚠ THE SCOPE DEPARTS FROM ROADMAP AND THE OPERATOR HAS NOT APPROVED IT. ROADMAP's U7 row says `sections, rail, filters, grid keyboard`. This contract drops sections and adds filename groups. The evidence is in `persistent-memory.d/2026-09-22-u7-remeasured-before-scoping.md`: zero of eleven gallery booths have a subdirectory, the only two booths that do are reports, and `pewpew-ui-brief`'s seven subdirectories hold one image between them. THIS IS THE ONE THING IN THIS DOCUMENT THAT IS A SCOPE-DIRECTION CALL RATHER THAN AN IMPLEMENTATION ONE, and it is his. THE GROUP HEURISTIC DEGENERATES, AND THAT IS A FIRST-CLASS CASE RATHER THAN AN EDGE. Measured: `sindra` yields ONE group for thirty images because every filename starts `00-`. A single group must render as NO rail rather than as a rail with one entry -- a navigation affordance that cannot navigate is worse than none, because it occupies the space where the real one would be. GROUPING IS A VIEW, NEVER A REORDERING. The item order stays `sorted(rel)` (U1 INV-3) and the zoom ring stays that order filtered to images. Grouping and filtering change what is SHOWN and never the sequence -- so `the third one` means the same thing with a filter on as with it off, and a flag lands where the operator thinks it does. This is the whole of CLAUDE.md invariant 6 applied to a surface that did not exist when it was written. THE PAGE WORKS WITH NO JAVASCRIPT. Filters are links with a query parameter, resolved server-side; the rail is anchors. Keyboard is the one genuinely JS-only affordance and it is additive -- the page is fully usable without it. U3 cost the verbatim path its no-JS operation and said so plainly; this unit must not quietly do the same to the gallery, which is the surface the operator actually reviews on. VIRTUALIZATION STAYS PARKED. The largest gallery is 66 images. ROADMAP parks progressive loading with `measure the real booth before optimising it`; at this size a lazy grid is almost certainly fine, and inventing the work is the failure the parking lot exists to prevent.	WHETHER THE GROUP HEURISTIC SHOULD BE OVERRIDABLE. A booth could carry a `.groups` dotfile naming its own grouping, the way `.blurred` names blur. Not designed here: no live booth wants it, the heuristic is right on four of five, and adding an override before anyone has been failed by the default is speculative. Parked, not solved. WHETHER `unanswered` AS A FILTER MEANS `has an open pick` OR `has no mark at all`. Both are useful and they are different questions; the first is the U4 hold predicate and already exists, the second is `show me what I have not looked at`. The rail names counts for both cheaply; the FILTER needs one of them chosen. Operator call, and it is small.

U7 — navigation at the size the booths actually are

⚠ PARTIALLY LANDED, DELIBERATELY.

component	ROADMAP says	state
sticky rail	ratified	landed — totals + per-filter counts, links not scripts
filters	ratified	landed — all / flagged / annotated / unanswered
grid keyboard	ratified	landed — ←/→ f n Enter Esc, bound only when a grid exists
sections → filename groups	departs from it	NOT BUILT. The one scope-direction call here, and it is the operator's. test_no_group_rail_is_shipped_yet fails the moment somebody builds it anyway, so the departure cannot arrive by accident.

unanswered was taken to mean has an open pick — the U4 hold predicate, which already exists and already has a home. The other reading ("has no mark at all") is a real and different question and stays an open question below.

The defect, re-measured rather than inherited

ROADMAP sizes this unit for 270 items. The largest gallery is now 81 items and 40 images. The four booths it was written against were swept on 2026-09-22 and the set churned again during that session. The defect is real and the sizing is not:

	ROADMAP's premise	measured 2026-09-22
largest gallery	270 images, one flat wall	sindra-bakeoff, 40 images
galleries with subdirectories	"sections come from subfolders, which already exist"	0 of 11
booths with subdirectories at all	—	2, and both are reports
grouping signal that does exist	—	the filename prefix

Sections are dead. The prefix is not.

Strip a trailing digit-run from each stem and group on what remains:

booth	images	groups
sindra-corpus-v1	66	16	ac01.png
sindra-nude-pool	42	12	flag-rear.png
sindra-sfw-pool	59	10	a01.png
sindra-bakeoff	40	5	00-sheet-c1-market-noon.png
sindra	30	1	00-b1-sheet-1.png — degenerates

Four of five. The competing heuristic — split on the second hyphen — yields 59 "groups" from 59 files and is useless everywhere. The degenerate fifth is the case the design has to carry, not the case that invalidates it.

What ships

1. Item.group — derived once, in the resolver, beside section.
2. A sticky rail — total, per-group counts, per-filter counts, jump-to-group anchors. Absent entirely when there is one group or fewer.
3. Filters — all / flagged / annotated / unanswered, as server-resolved query parameters so they work with JS off.
4. Grid keyboard — ←/→ move focus, f flags, n opens a note, Enter zooms, Esc clears focus. Additive; the page is complete without it.

Signatures

def _group_of(rel: str) -> str | None:
    """The grouping key for an item, or None when it has none.

    THE RULE: take the stem of the basename, strip ONE trailing run of digits
    and any single separator before it, and return what remains. `ac01.png` →
    `ac`; `00-sheet-c1-market-noon.png` → `00-sheet-c1-market-noon` (no
    trailing digit run, so the whole stem); `flag-rear.png` → `flag-rear`.

    Returns None for a stem that is ENTIRELY a digit run — `01.png` has no
    prefix to group on, and inventing one would put every numbered file in a
    group named after the empty string.

    Derived HERE and nowhere else (INV-1). A route body that re-derived it
    would be the caption bug in a new field.
    """

Ordering — the rule, because invariant 6 binds

collection	rule
items	unchanged — sorted(rel) (U1 INV-3)
the zoom ring	unchanged — item order filtered to images
groups among themselves	the position of each group's FIRST member in sorted(rel) — so the rail reads in the same direction the grid does, and adding a file never reshuffles the rail unless it lands first in its group
items within a group	unchanged — they are a filtered view of sorted(rel), never re-sorted
the filtered grid	unchanged — sorted(rel) with non-matching items hidden

This closes ROADMAP's outstanding U7 order question. Compare pairing is not this unit's problem — compare mode is parked to v1.1 with the pairing rule.

Invariants

INV-1 — one resolver derives the group. _group_of is called only from booth_items. Falsifiable: the defeating change is a route or template computing a prefix inline. The test asserts no call to _group_of survives inside create_app — the same assertion U1 makes for classify and render_doc, which is why it is the shape used here.

INV-2 — grouping and filtering never reorder. Falsifiable: the defeating change is sorting by (group, rel) to make the grid render contiguously, which looks right and silently changes what "the third one" means. The test renders a booth whose groups interleave in sorted(rel) order and asserts the rendered item sequence is byte-identical with grouping on and off, and that image_chain is unchanged under every filter.

INV-3 — one group renders NO rail. Falsifiable: the defeating change is {% if groups %}, which is true for a single group. The test uses the real sindra-shaped fixture (thirty files, one prefix) and asserts the rail element is absent — not merely that it lists one entry.

INV-4 — a filter is a link, not a script. Falsifiable: the defeating change is binding filters to a click handler. The test fetches the filtered URL directly and asserts the server returned the filtered grid, with no JS executed.

INV-5 — the keyboard never fires on a booth with no grid. Falsifiable: the defeating change is binding the handler unconditionally, so f on the standing link board flags nothing and swallows the keystroke. The test asserts the handler is not bound when items is empty.

Out of scope

• Sections as a rail. Measured worthless; Item.section is untouched.
• Compare mode. Parked to v1.1 with its pairing rule.
• Virtualized loading. Parked; measure first.
• A .groups override file. See open questions.
• Anything on the verbatim path. It has no grid.