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Defer LRD blank-line pop to next-line baseline#677

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Defer LRD blank-line pop to next-line baseline#677
stefanobaghino wants to merge 34 commits into
trishume:masterfrom
stefanobaghino:631-markdown-lrd-blank-line

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A non-terminated Markdown link reference definition title spanning a
content line and a following empty line had its meta_scope collapsed
on the wrong line boundary. Without the fix, the chained
link-title-continuation + link-def-attr-continuation exhaustion
emitted the LRD pop on line 2's \n (= line 3's stack baseline),
dropping meta.link.reference.def.markdown on the empty line. ST
emits that pop one boundary later (between line 3 and line 4).

Two-part guard in src/parsing/parser.rs:

  • parse_next_token: skip a non-consuming Branch whose match lands
    at or past the replay line's end when inside replay_ctx. Prevents
    a chained branch_point from being created at end-of-replay-line.
  • handle_fail same-line path: when the rewind position is 0 of an
    empty line (length ≤ 1, just \n), advance the cursor to
    line.len() so a follow-up match: '' pop: N emits past-EOL.
    ScopeRegionIterator wraps that to the next line's baseline.

Baseline: Markdown 1 → 0 (syntax_test_markdown.md row removed from
testdata/known_syntest_failures{,_fancy}.txt). No other rows change.

Stacked on #676. Isolated diff:
stefanobaghino/syntect@631-zsh-range-clear-parent-string-scope...631-markdown-lrd-blank-line

`handle_fail` already re-emits the branch_point match's `pat.scope`
so a keyword like `LIKE` retains its scope after a branch swap. It
did not do the same for `captures:`-derived scopes, because those
are computed from the match's `regions` at emit time and not stored
on the BranchPoint record. On same-line and cross-line fail paths
the original capture Push/Pop pair was truncated off `ops` together
with alt[0]'s subsequent work and never replayed.

Minimal Haskell repro:

    data CtxCls ctx => ModId.QTyCls
--  ^^^^ keyword.declaration.data.haskell

The `datas` branch_point match is
`(data)(?:\s+(family|instance))?` with
`captures: { 1: keyword.declaration.data.haskell, 2: storage.modifier.family.haskell }`.
When `data-signature` (alt[0]) fires `fail: data-declaration` on
the `=>` lookahead, replay into `data-context` (alt[1]) only
restored `scope: meta.declaration.data.haskell` — the `data` token
lost its inner `keyword.declaration.data.haskell` scope.

Fix: snapshot the computed capture ops on the BranchPoint record
at creation time (new `capture_ops` field), and replay them inside
the pat_scope brackets in both fail paths. Extracts the capture-op
build logic (previously inline in `exec_pattern`) into a
free-function helper `build_capture_ops` used at both call sites.

Regression test `branch_point_capture_scopes_survive_fail_retry`
mirrors the Haskell shape with a synthetic two-alt branch whose
trigger match carries both `scope:` and `captures:`.

Syntest net:
- Haskell/syntax_test_haskell.hs: 72 -> 50 (Cluster A closes;
  `data CtxCls ctx => …`, `data family … => …`, and
  `type … => …` all now retain their declaration-keyword scope —
  22 assertions).
- No collateral deltas on any other baseline file (both regex
  backends).

Refs: trishume#631
Mechanical: Haskell drops from 72 to 50 failing assertions on both
regex backends. No other baseline lines change.
- Inline `build_capture_ops` signature so it fits on one line under
  the older rustfmt in CI's Minimum supported rust version job.
- Escape `alt[0]`/`alt[1]` in the `BranchPoint.capture_ops` doc so
  rustdoc stops treating them as intra-doc links under `-Dwarnings`.

Refs: trishume#631
push_meta_ops emitted the compound Pop before the Restore when the
leaving context carried `clear_scopes:` and `set_pop_count > 1`. The
intermediate popped frame's meta_content_scope is split across the
live scope stack and clear_stack; Pop — counting the full pre-Clear
total — then ate atoms from frames below the popped range.

Observed on Batch File `cmd-set-quoted-value-inner-end`
(`clear_scopes: 1`) firing `pop: 2, set: ignored-tail-outer`, which
dropped `meta.command.set.dosbatch` from the trailing content of every
quoted `set "var"=...` line.

Emit Restore before Pop when `set_pop_count > 1`; plain `set:` keeps
the existing Pop-then-Restore order (gated by the Lisp `defun` test
`v2_set_to_target_with_clear_scopes_clears_parent_meta_content_scope`).

syntax_test_batch_file.bat: 74 → 0 on both backends; no other baseline
entry changes. New regression
`pop_n_set_with_cur_clear_scopes_restores_before_popping_deeper_frames`.

Refs: trishume#631
Sublime Text applies `captures: N:` to the overlap between group N's
span and the rule's consumed match range. syntect dropped lookaround-
internal captures in `parse_captures` and would have emitted Pop past
match_end in `build_capture_ops` had they reached it.

Keep every non-negative `captures:` key at load time; clip
`(cap_start, cap_end)` to `regions.pos(0)` at apply time. Removes the
now-unused `get_consuming_capture_indexes` walker and its tests.

Baseline (both backends): clears
ASP/syntax_test_asp.asp (53), C#/tests/syntax_test_Generics.cs (3),
Rails/tests/syntax_test_rails.html.erb (23).

Refs: trishume#631
ST drops the popped context's `meta_scope` and `meta_content_scope`
from the trigger match's text for `pop: N + embed:`, unlike
`pop: N + set:` which preserves both. Rules in the wild re-add the
meta_scope atom explicitly in their match `scope:` so it still
appears exactly once on the trigger — HTML (JSP).sublime-syntax's
`tag-jsp-{declaration,expression,scriptlet}-attributes` all do.

syntect's Embed → synthetic Set routing in `push_meta_ops`
inherited plain-Set semantics, so cur.meta_scope stayed on the
stack and the match's explicit scope duplicated it on top.

Fix: when `pop_count > 0`, emit initial-phase Pops for cur's mcs
and ms, then pass a scope-stripped clone of cur through to the
recursive Set call so its non-initial `num_to_pop` doesn't
double-account atoms that are already off the stack. Probe and
ordering invariant in `v2_pop_embed_suppresses_cur_meta_scope_on_match`.

Net syntest: Java/jsp 44 → 39 on both baselines (5
`- meta.tag.jsp meta.tag.jsp` assertions cleared). The other 39
are three unrelated root causes, not addressed here.

Refs: trishume#631
A cross-line `fail` replay commits a Push(meta_scope) to
`flushed_ops` for a speculative context; a later same-line `fail`
for a branch_point created *during* the replay then truncates the
owning context out of `self.stack` without emitting a balancing
Pop (the Push is in `flushed_ops`, beyond `ops.truncate`'s reach).
`exec_escape` pops based on the truncated stack, leaving an
orphan atom at the top.

Track a `shadow: ScopeStack` mirror of the consumer view, synced
at `parse_line` boundaries the same way `syntest` applies
`replayed` + `ops`. `exec_escape` now emits a corrective Pop for
any atoms exceeding the sum of `self.stack`'s `meta_scope` /
gated `meta_content_scope` contributions.

Drops `syntax_test_latex.tex: 76` from both
`testdata/known_syntest_failures{,_fancy}.txt`.
`IncludeWithPrototype` in `MatchIter` pushed the included target
on top of the prototype, and `MatchIter::next` reads the stack
top (`ctx_stack[len-1]`) — so the target's patterns were iterated
first and the external prototype's second. The parser's
tie-break on match_start is strict `<`, so whichever rule is
enumerated first wins a same-position match.

ST's `apply_prototype` semantics and `ParseState::find_best_match`'s
own `context.prototype` chaining (`chain(cur_prototype).chain(cur_context)`)
both put prototype patterns ahead of the target. Swap the two
pushes so the prototype lands on top of the stack and is iterated
first.

Concretely: in HAML `tag-attributes-content`, `ruby-code` does
`include: scope:source.ruby.rails.embedded.haml apply_prototype: true`.
Ruby-for-HAML's prototype injects HAML's `pipe-continuations`
(match `|\s*$`). Before this fix, Ruby's bitwise-or rule
(`[~|^]`) at the same position was iterated first and won the
tie, so `|` at EOL got `keyword.operator.bitwise.ruby` instead of
`punctuation.separator.continuation.haml`; the attribute braces
popped at the newline, and every continuation assertion below
cascaded. After the swap, the prototype's pipe-continuation wins
the tie.

Refs: trishume#631
Strengthens the existing `apply_prototype_includes_external_prototype`
from build-only to parse-and-assert. Adds precedence, opt-out, and
HAML-Rails end-to-end guards alongside it in `src/parsing/syntax_set.rs`.

Refs: trishume#631
All 65 assertions in `syntax_test_rails.haml` pass after the
apply_prototype ordering fix. Delta applies to both baselines.
ST's `text_point(row, col)` overflows past-EOL columns into the next
row, so its syntax-test framework evaluates past-EOL assertions
against the corresponding column on the next line. syntect's harness
was instead testing against the consumed `\n`'s scope — silent
divergence whenever the `\n` carried parent meta_scopes that the EOL
pop chain dropped.

Reorder the loop to parse-before-assert; thread the first post-target
line's scopes into `process_assertions` (`examples/syntest.rs`); fall
back to the previous behaviour when next-line scopes aren't available
(EOF, replay path). Closes 17 `syntax_test_git_config` and 1
`syntax_test_clojure` stale baselines. Refs: trishume#631
Two cross-line branches failing on the same parse_line grew
`flushed_ops` by append, so `ParseLineOutput::replayed` doubled and
consumers that pair `replayed[i]` with the i-th pending line slid
ops from one buffered line onto another's text. Observed as the
byte-77 panic at `syntax_test_java.java` line 624.

Track `flushed_ops_start` alongside `flushed_ops` and merge
subsequent fails against the prior snapshot's range. See
`ParseState::merge_flushed` docs for the composition rule.

`known_syntest_failures{,_fancy}` absorb the unmasking: Python /
TypeScript / Bash / Zsh files previously panicking now report their
real path-1 counts. Java stays at `1` — next panic site is a
pre-existing stale-`line_number` on branches created during replay,
tracked as follow-up. Refs: trishume#631
Branches created while `handle_fail` re-parses a buffered past line
snapshotted `self.line_number` / `self.pending_lines.len()`, which
still reflect the *outer* `parse_line`'s current line. A later fail
on the outer line would then see `bp.line_number == cur_line`,
classify the branch as same-line, and apply the branch's
replay-line-relative `match_start` to a shorter outer line —
shipped as `byte index 20 out of bounds of "  foo = BAR,\n"` on
`syntax_test_java.java:10263` inside `@MultiLineAnnotation(...)`,
and the matching byte-2 panic in `syntax_test_markdown.md`'s
multi-line math blocks.

Introduce a `replay_ctx: Option<ReplayCtx>` set around each inner
`parse_line_inner*` call in both replay loops. Branch creation and
`handle_fail`'s `cur_line` read through it, so branches born in the
re-parse of line `L+i` record `line_number = L+i` and
`pending_lines_snapshot_len = <slot for L+i>`.

Baselines absorb the unmasking: TypeScript drops 230 to 12
(cascading replay-branch misclassifications fixed), Markdown moves
1 to 897 (the `1` was the byte-2 panic artefact; real count
surfaces). `syntax_test_java.java` stays at `1`: a distinct
pre-existing `NoClearedScopesToRestore` surfaces further into the
same file, tracked as a follow-up.

Refs: trishume#631
A `branch_point` born inside `handle_fail`'s cross-line replay
recorded only the inner re-parse's local `res` Vec as its
`prefix_ops`. When that nested branch later failed cross-line, its
own replay reconstructed the line from an empty prefix and the
captures emitted before the *outer* branch trigger vanished.

Shipped as `[foo]: /url` losing its
`meta.link.reference.def.markdown` and capture scopes whenever the
outer `link-def-title-continuation` branch's `immediately-pop2`
alt-1 spawned a nested `link-def-attr-continuation` whose own fail
then replayed line 3 without the original LRD opener captures.

Compose the first-line prefix (outer `prefix_ops` + new-alt
meta/pat/capture/meta_content) up front in both cross-line replay
paths, surface it via `ParseState::replay_prefix_ops`, and
prepend it to inner branch creations' `prefix_ops`.

Baselines: Markdown 897 → 565, TypeScript 12 → 0 (file disappears
— `syntax_test_typescript.ts` exercised the same nested-replay
shape).

Refs: trishume#631
`parse_line` captured the buffered shadow snapshot BEFORE the line
ran, and the syntest consumer captured `stack_before` similarly. A
replay applied during that line's parse may have corrected ops for
prior buffered lines, leaving the captured snapshot reflecting the
uncorrected baseline. A LATER replay covering the same line then
resets to that stale snapshot, re-applies the corrected ops on top,
and resurrects any meta_scope the prior replay had unwound.

Manifested as `meta.link.reference.def.markdown` leaking past
back-to-back Markdown link reference definitions and polluting all
subsequent paragraphs, code blocks, blockquotes, autolinks, footnotes,
etc. for the rest of the file (~408 chars / 88 assertions in
`syntax_test_markdown.md`).

After applying replays in `parse_line`, overwrite each buffered
`pending_line_start_shadows[start_idx + i + 1]` with the post-i
shadow, and use the post-replay shadow as the snapshot for the
current line being pushed. Mirror the same correction in `syntest`'s
consumer loop on `parsed_line_buffer[..].stack_before`.

Baselines:
- Markdown 565 → 158 (the LRD-leak family)
- Java 1 (panic) → 18953 (real failures unmasked — the
  `NoClearedScopesToRestore` panic that the same drift was
  triggering is gone)

Refs: trishume#631
A `pop: N + branch_point` snapshots `stack_depth` pre-pop; the synthetic
Set's post-Set retain (`bp.stack_depth <= final_len`) and `handle_fail`'s
validity check (`stack.len() < bp.stack_depth`) both ignored that
`pop_count`, dropping the freshly-created bp at creation. Same-line
re-emit also missed the popped contexts' meta_scope clearance Pop —
route it through `push_meta_ops` like the original push.

Symptom: `meta.annotation.identifier.java meta.path.java` leaking past
nested-annotation extends paths in `syntax_test_java.java`. Drops
Java baseline 18953 -> 9956.
Mirrors the trishume#660 same-line fix into the cross-line branch — the
bespoke re-emit of the new alternative's meta_scope/meta_content_scope
was missing the popped contexts' Pop, leaking the popped meta_scope
(annotation-qualified-identifier's meta_scope in Java) plus the
surrounding declaration's meta_scope when an annotation crosses a
line into a class/enum/interface declaration.
…ctions

When an outer cross-line `fail`'s replay re-parses buffered lines, an
inner cross-line `fail` firing during the loop writes its correction
into `self.flushed_ops`. Previously, the outer's locally-computed
`replayed_ops[i]` overwrote that correction via `merge_flushed`, freezing
a stale interpretation for indices the inner had already corrected.

Fixes the leak in `src/parsing/parser.rs::handle_fail` for both the
alt-N and exhaustion cross-line paths. Repro: Java
`@A.B\n(par=1)\nenum E {}\n` — the outer `declarations` fail's line-1
reparse froze the dotted annotation as `path` alt before the inner
`annotation-qualified-identifier` fail's `name`-alt resolution landed.

Drops Java syntest baseline 9935 → 9774; no regressions in other
languages or in `Markdown` (still 158).
When a same-line branch_point exhausts at a zero-width
lookahead, rewind the cursor to the BP's original position
and skip the same-name Branch pattern on retry — letting the
parent context's next rule fire instead of advancing past the
lookahead, which let stale keyword rules match inside
identifiers (`package` in `$package`, `class` in `Foo.class;`).

Drops Java syntest 9774 → 1987 (-7787, -80%); jsp 39 → 0; Zsh
604 → 410. Markdown unchanged at 158. No regressions
elsewhere.

See parser.rs::handle_fail same-line exhaustion handler and
the new `skipped_branches` field; new test
`exhausted_branch_point_falls_through_to_parent_next_rule`.
`push_meta_ops`'s non-initial phase emitted the deep-context
meta_scope/mcs Pops before restoring `cur_context.clear_scopes`.
When the cleared atom belonged to one of the deeper contexts
being popped, the Pops landed on the wrong (still-visible)
scope — observed on Java's `case DayType when -> "incomplete"`,
where `case-label-expression`'s `clear_scopes: 1` hid
`case-label`'s `meta.case.java` and `case-label-end`'s
`pop: 2` then popped the surrounding switch block off the
consumer's stack.

Move the cur_context Restore to before the depth loop so the
previously-cleared atom is visible again when the deeper-context
Pop lands on it.

Drops Java syntest 1987 → 949 (-1038, additional -50%); fixes
C#'s `syntax_test_GeneralStructure.cs` (was 2 → 0) and
Haskell -1. Markdown unchanged at 158, no other regressions.

See `parser.rs::push_meta_ops` Pop arm and the new test
`pop_n_restores_clear_before_unwinding_deeper_meta_scopes`.
The YAML loader checked `set:`, `branch:`, and `embed:` after a `pop:`
key but never `push:`. Combined `pop: N + push: X` rules degraded to a
plain `Pop(N)` and silently dropped the push, leaving the parser on the
outer context instead of the intended target.

Affected rules in vendored syntaxes: Java's
`pop: 2 + push: annotation-parameters-body` (lambda3 line 10069 and
many others) and `pop: 1 + push: case-label-expression`; Python's
`pop: 2 + push: function-parameter-list-body` and `type-parameter-list-body`.

Java syntest 641 → 245 (-396); Python 66 → 45 (-21). Other language
baselines unchanged.
The Set initial-phase Pop at parser.rs:1992 unconditionally popped
`cur_context.meta_content_scope.len()` even when cur_context's mcs
was never pushed because the context immediately below has
`embed_scope_replaces=true`. This dropped the topmost wrapper-pushed
embed_scope token. Mirrors the skip already in the Pop branch at
parser.rs:1912.

Markdown 158 -> 31; Python 45 -> 32 (free benefit).
Plain `set:` (no `pop_count`) into a target with `clear_scopes`
emitted that Clear in `push_meta_ops`'s initial phase even when the
leaving context carried its own `meta_scope` / `meta_content_scope`.
Cur's ms sits on top of the visible stack at that point; Clear hid
it instead of the parent atom the optimization was meant to strip.
The non-initial Pop then ate atoms below cur's hidden ms, and the
trailing Restore resurrected cur's ms — leaving cur's meta_scope
where the parent's atom used to be.

Bash repro `: ~/`: `~` set: `tilde-modifier` (clear+ms); `''`
zero-width set: `tilde-modifier-username` (clear+mcs); `/` lookahead
pops. ST scopes `/` as `meta.string.glob.shell string.unquoted.shell`;
syntect emitted `meta.interpolation.tilde.shell string.unquoted.shell`.

Fix: when cur has `meta_scope` or `meta_content_scope`, defer the
single-context-set target Clear to the non-initial phase, after
Pop+Restore (so Pop finds cur's ms visible and Restore brings the
parent atoms back) and before pushing target's ms/mcs. The cur-empty
case (Lisp `(defun fn (...)`, pinned by
`v2_set_to_target_with_clear_scopes_clears_parent_meta_content_scope`)
is unchanged.

Net syntest: bash 249 → 30, zsh 410 → 25, java 245 → 221 on both
regex backends; no other baseline lines change. New regression
`cur_meta_scope_set_to_target_with_clear_scopes` mirrors the bash
shape.

Refs: trishume#631
Multi-context `set:` whose target body has both `clear_scopes: N` and
a non-empty `meta_scope`, fired from a cur with no ms/mcs/clear,
needs an extra atom dropped on the trigger token beyond Clear's
reach. ST drops `N + 1` atoms on the trigger and `N` on the body
content, anchoring the extra drop on the target's `meta_scope`.

`push_meta_ops` previously kept both atoms on the trigger, leaking
nested `meta.function.php` / `meta.function.return-type.php` into
the `:` of PHP `function bye(): never {`. The fix emits a combined
`Clear(N + 1)` in the initial phase and a paired `Restore` in the
non-initial phase, leaving the body content's existing per-context
Clear+Push to land it at the same place as before.

Gated on the clear-bearing target carrying a non-empty `meta_scope`
so syntaxes whose target has only `meta_content_scope` are
unaffected — Zsh's `zsh-redirection-glob-range-end` (clear+mcs, no
ms) on the `<` redirection trigger otherwise loses
`source.shell.zsh` and `meta.function-call.arguments.shell`.

PHP 1 -> 0.
push_meta_ops's `MatchOperation::Set` arm with `set_pop_count > 1`
lumped target.ms + cur.ms + every popped deeper frame's mcs+ms
into a single Pop. Per-frame clear_scopes were never restored —
their cleared atoms stayed in clear_stack out of reach, and the
new target's clear_scopes then bit one atom too deep.

Observed on Python `r'''(?ix:some text(?-i:hello))(?iLmsux)(?a)foo'''`:
the `(?ix:` rule's `pop: 3 + set:[group-body-extended,
maybe-unexpected-quantifiers]` left `group-body-extended_outer`'s
cleared `meta.mode.extended.regexp` in clear_stack;
`group-body-extended_target`'s `clear_scopes: 1` then cleared
`source.regexp.python` (the embed wrapper's mcs) instead of
`mode_outer`. ST keeps `source.regexp.python` visible from col 22
through col 47+; syntect previously dropped it from col 27 onward.

Split the lumped Pop into a head Pop (target.ms + cur.ms) and a
per-depth Pop+Restore loop mirroring `MatchOperation::Pop` arm at
parser.rs:1954-1971. New regression tests
`pop_n_set_restores_deeper_frame_clear_scopes` (positive) and
`pop_n_set_without_deeper_clear_scopes_unaffected` (negative gate
against regressing Java's `pop:2 + push:annotation-parameters-body`
shape).

Refs: trishume#631
Resolved by per-depth clear_scopes Restore on pop:N + set:.

Refs: trishume#631
`yaml_load`'s `parse_embed_op` was setting `embed_scope_replaces=true`
on the wrapper unconditionally. That flag tells the per-target loop in
`parser.rs` to suppress the next context's `meta_content_scope` push,
to avoid duplicating the embedded syntax's top-level scope (auto-
inserted into `main`'s mcs at `yaml_load.rs:706-713`) with the
wrapper's last `embed_scope` atom.

That dedup is only needed when the embed enters via `main`. Fragment
embeds (e.g. `embed: scope:source.toml.embedded.python#toml`) bypass
`main`, so the fragment context's mcs is independent of the syntax's
top-level scope. Suppressing it strips a real grammar atom (TOML's
`meta.mapping.toml`) and the next `clear_scopes:` then bites the
wrapper instead of the intended grammar atom — leaking the wrapper
out of every nested scope inside the embed.

Mark the wrapper as `embed_scope_replaces=true` only when the embed
target has no `#fragment`. Two regression tests:
- `fragment_embed_preserves_target_meta_content_scope` (positive)
- `non_fragment_embed_still_suppresses_main_mcs` (negative gate)

The b31b727 test
`embed_scope_replaces_preserves_wrapper_mcs_across_inner_set` is
unaffected — Markdown's bash code-fence embed has no fragment.

Python 32 -> 0 on both regex backends; no other baseline moves.
When a child syntax has multiple parents in `extends:` and the parents
disagree on a shared context or variable, a parent's directly-defined
entry now outranks another parent's inherited entry. Same-provenance
ties still resolve last-wins.

Fixes the indented zsh shebang in Markdown fenced blocks: `Zsh (for
Markdown)` extends `[Bash (for Markdown), Zsh]`. Bash (for Markdown)
owns a lenient `main` (`^(?=\s*#!)`); Zsh inherits Bash's strict
column-0 main. The previous last-wins merge let Zsh's inherited main
override, so the indented `   #!/usr/bin/env zsh` fell into the
regular comments rule.
`get_line_assertion_details` recognised any line where the testtoken
appeared mid-text and where valid assertion markers followed. ST's
syntax-test format only allows assertions on dedicated comment-only
lines, so source code preceding the testtoken means the markers are
coincidental. The harness was processing such lines as assertions
anyway, producing spurious failures and pinning
`test_against_line_number` away from the source line so the *next*
genuine assertion tested against stale scopes.

Fix: early-return `None` when source code precedes the testtoken or
non-whitespace follows the closing testtoken_end. The two bash repros
are `: ${#^pattern}` (the `#` is the parameter-length operator) and
`[ <<doc ]  # <- ]` (a trailing comment whose body starts with `<-`).

Doing this also exposed a latent bug in
`only_whitespace_after_token_end`: `after_token_end` was the substring
*from* the end-token, so the end-token glyphs themselves always
counted as non-whitespace, and `/* ^ scope */` lines were silently
classified as non-pure. Under the old gate this was harmless (the
flag only fed the `parse_test_lines` path), but the early-return
turned every C-style block-comment assertion into a non-assertion
source line. Skip the end-token before checking the trailing content.

Three new harness unit tests cover the corrected predicate and both
shell repros. Two existing tests already exercise the pure-assertion
path; their `is_pure_assertion_line` field assertions are now
invariant-true at the constructor, but kept as documentation.

Net syntest deltas (both regex backends):
- Bash 30 -> 4 (residual: backtick `for...done` interaction)
- Zsh 25 -> 10 (residual: zsh glob-range scoping)
- Haskell 49 -> 43

Stacks on trishume#673.
The per-line search cache stored full-line `regex.search` results keyed
by MatchPattern pointer, then reused them on every later search regardless
of `search_end`. Inside an embed where `search_end` is clipped to the
escape position, that reuse can flip rule outcomes whose lookaheads sit
exactly at the boundary — the cached "no match" was computed against the
escape glyph, but a fresh truncated search would see end-of-input there.

Concretely: in `` `for i in $(seq 100); do echo $i; done` `` the
`done{{cmd_break}}` rule (`done(?!cmd_char)`) was searched at the outer
level with full-line text, where the lookahead saw the closing backtick
(itself a cmd_char) and failed. That `None` was cached. Inside the
backtick embed, with search_end clipped to the close, the cache
short-circuited the lookup before the regex could re-run with
end-of-input semantics, so `done` fell through to `cmd-name-body` and
got `variable.function.shell` instead of `keyword.control.loop.end.shell`.

Skip the cache lookup whenever `search_end < line.len()`. Insertion was
already gated on `search_end == line.len()`, so the cache stays
populated by full-line answers; truncated searches just re-run.
In a multi-context `set:` whose non-topmost target declares
`clear_scopes: N` plus a `meta_content_scope`-only body (empty
`meta_scope`), Sublime applies the Clear to atoms that earlier targets
pushed via their `meta_scope` and the strip is visible to the trigger
match's own scope/captures. Syntect was deferring the Clear to the
non-initial phase, so the trigger token leaked the cleared atom even
though body content saw it removed.

Surfaces on Zsh glob-range openings inside `[ <1-2> ]` etc.: the
`zsh-redirection-glob-range-begin` `set:` lists `string-path-pattern-body`
(meta_scope `meta.string.glob.shell string.unquoted.shell`) before
`zsh-redirection-glob-range-end` (`clear_scopes: 1` +
`meta_content_scope: meta.range.shell.zsh`), and the `<` carries a
capture scope asserted with `- string`. Drops the residual 10-char Zsh
syntest failure on both backends.
Two-part guard against `branch_point` exhaustion collapsing a parent
`meta_scope` one line boundary too early on empty lines:

1. In `parse_next_token`, a non-consuming `Branch` match that lands at
   or past the replay line's end is skipped when inside `replay_ctx`.
   Without this, the outer fail-replay would chain another `branch_point`
   at end-of-replay-line whose own cross-line exhaustion later attaches
   pops to the wrong line.
2. In `handle_fail`'s same-line path, when the rewind position is 0 of
   a purely empty line (length ≤ 1, just `\n`), advance the cursor to
   `line.len()`. The next-iteration `match: ''` of an `immediately-pop`-
   style alt then emits its scope pops past-EOL, which
   `ScopeRegionIterator` wraps onto the next line's baseline.

Together they make Markdown's non-terminated link reference definition
keep `meta.link.reference.def.markdown` on the empty line between
`blah` and the closing `text` paragraph, matching ST.

Baseline: Markdown 1 → 0 (the `syntax_test_markdown.md` line drops
from `known_syntest_failures{,_fancy}.txt`). No other rows change.
@stefanobaghino
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CI failures looks due to a transient failure when grabbing Zig from Codeberg (same check on #678 succeeded), but I don't seem to have the permissions to restart it.

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