libyaml refuses to skip a tab in the inter-token whitespace whenever a
simple key is allowed, so a tab used as valid separation (after a '-',
'?', or ':' indicator, or before a flow collection) is reported as a
character that cannot start a token. But a tab is legal in-line
separation; it is only illegal as indentation.
The scanner now skips tabs in scan_to_next_token and records in
tabbedSeparation whether one preceded the pending token. A block entry,
an explicit key, or an implicit mapping key promoted by ':' is rejected
when reached through a tab (there the tab would be indentation), while a
scalar value or a flow collection is accepted. Tab-indented keys and
'-\t-' nested entries still reject.
Surpasses libyaml on 6BCT, 6CA3, A2M4, DK95/00, Q5MG, Y79Y/010.
Port score 299 -> 305.
YAML 1.2 lets a flow-context key be separated from its ':' value indicator
by line breaks, so a flow-level simple key must survive a new line (it is
still bounded to 1024 characters). libyaml invalidates every simple key on
a new line, which wrongly rejects keys like `{"foo"\n: "bar"}` and
multi-line quoted keys.
Canonical event conformance: 259 -> 268 of 308 (4MUZ/00-02, 5MUD, 9SA2,
K3WX, NJ66, UT92, VJP3/01). This passes the hand-rolled parser's 267 and
exceeds libyaml's own 252. 333 tests pass.
Stage 3 of the faithful libyaml scanner port: the token producer. Translates scan_to_next_token, fetch_more_tokens/fetch_next_token dispatch, and the fetchers for stream start/end, document indicators, block entry, key, value (with the simple-key splice and roll-indent), plus scan_plain_scalar with its line-break folding. Reuses the ported indent engine, simple-key mechanism, character classes, and reader. Constructs not yet ported (flow collections, quoted scalars, anchors, tags, directives, block scalars) throw an explicit 'not yet ported' error rather than mis-scan; the port is not yet wired to the public API.
Milestone: the ported scanner tokenizes '- a:' followed by a same-column 'b:' as siblings (one BLOCK-MAPPING-START), matching libyaml, fixing the original block-mapping bug by construction; a more-indented value still nests. Unit-tested for the sibling case, the nested case, a simple pair, and multi-line plain-scalar folding. 305 tests, no regression.
Stage 2 of the faithful libyaml scanner port. Translates yaml_parser_save_simple_key, yaml_parser_remove_simple_key, yaml_parser_stale_simple_keys, and the flow-level push/pop (yaml_parser_increase_flow_level / decrease) onto a new PureYAML.Parsing.LibYAML.Scanner aggregate that embeds the indent engine. The simple-key mechanism is what lets a quoted scalar, a nested collection, or a property-carrying node become a mapping key when a ':' follows, and is required exactly at the block indent. Modelled faithfully: a potential key goes stale once it spans a line break or exceeds 1024 characters, and a required key that is removed or goes stale is the 'could not find expected colon' error. Unit-tested for the required/not-required, removal-error, staleness, and flow-level cases. No public behavior changed yet.
