DOG-026: MKDT meta-pair leaf block `Key: value`

Now: DONE

Tickets now carry meta (assignee, due date, milestone) as Key: value lines under the header, per todo; the leaf is specced in StrictMark §"Meta pairs". The tokenizer must emit it as its own block type so renderers and view verbs stop reading meta as paragraph prose.

Input

Context

Spec: KEY ':' GAP VALUE, KEY := [A-Z][a-z][a-z] at line start; value verbatim to EOL, no inline layer.
Registered ticket keys (todo): Who: Due: For: Ask: Env: Rev: Dup: Sub:; the grammar is key-agnostic.
Today such a line lexes as paragraph text: greps work, but rendering and the :todo view (BE-038) see prose.
Ticket status moves from the header into a meta pair (ruling 2026-08-02), so this leaf carries the board's primary query, not just decoration.
The meta-pair index TODO-003 extracts by line regex until these tokens land, then swaps over; its row carries a 4-bit kind, so the lexer's kinds are what it can index.

Goals

MKDTLexer (dog/tok/MKDT.c) emits a distinct meta-pair leaf token for ^[A-Z][a-z][a-z]: lines.
A line-start escape (Due\:) keeps a paragraph a paragraph; StrictMark-wins otherwise.
Repro-first: fixture with a ticket header + meta block + prose-with-colon lines, asserting token kinds.
Each indexable leaf carries a distinct kind nibble — meta pair now, -[ ] todo marker next for the board badge (TODO-002) — one shape the index can key on.

Constraints

New alternative in the line-start scan before the paragraph fallback; ragel/regex, no hand-rolled byte scanner.
Marker is exactly 4 chars (Who: + gap), consistent with the DOG-024 quad discipline.
Renderer support (key–value row in mark) is a separate MARK ticket once tokens land.

WIP

Design decisions

Shape-only recognition: key vocabulary lives in todo, never in the lexer.

TODOs

meta-pair token kind + lexer alternative in dog/tok/MKDT.c
\: line-start escape (free: the backslash breaks the quad shape, test asserts it)
tokenizer tests: meta block, prose false-positive, escape (MKDTMetaPairTest in test/TOK01.c)
todo-marker leaf kind for the board's progress badge (TODO-002)
stable per-leaf line/offset for TODO-003's line field (moot: the kv64 redesign dropped the line field)
file the MARK renderer follow-up ticket
StrictMark §"Meta pairs" grammar line: widen [A-Z][a-z][a-z] to [A-Z][a-z][a-z0-9] (On1: ruling 2026-08-03)

Blockers and bummers

Outcome

Landed in the main tree 2026-08-03 (explicit order), uncommitted; suggested commit DOG-026: meta-pair leaf Key: value in MKDTB.

Grammar: meta = (upper lower (lower|dig) ':' @mt_run) >mt_start sp @mt_set in the innermost list position of main := (tok/MKDTB.c.rl), MKDTB.rl.c regenerated (ragel 6.10).
mkdtblock gains meta/metakey (tok/MKDT.h); lexer emits key quad 'T', value one verbatim 'S' (no inline layer), 'W' newline; a meta line ends a paragraph run (tok/MKDT.c).
ctest 72/72 green, new test failed pre-port (repro-first); prior work/DOG-026 wt superseded by this port + digit widening.

DOG-026: MKDT meta-pair leaf block Key: value