feat(lang): add IEC 61131-3 Structured Text (.st)

[SarletteD]

Refs #1810. Stacked on #2396 (prerequisite style(mcp): compare nullable strings through one helper,
branch fix/cppcheck-nullable-strcmp); until the prerequisite merges, this PR also shows its commit.
This is the first of four Structured Text PRs (1a language, 1b dialect normalizer, 1c export layout,
1d real-world dialect).

What does this PR do?

Adds IEC 61131-3 Structured Text as CBM_LANG_ST on .st, with the vendored grammar
HeytalePazguato/tree-sitter-iec61131-3-st
@ 00e24f50f8de (MIT, (c) 2026 Jorge Centeno), and the ST-specific extraction the graph needs:

• lang_specs.c: node types for functions/methods (method_signature for INTERFACE members), the
  class-like POUs (FUNCTION_BLOCK, PROGRAM, INTERFACE, type_definition), properties, calls
  (call_expression, invocation_statement), USING imports, branches, variables, assignments.
• extract_defs.c: every base of EXTENDS/IMPLEMENTS is collected by st_base_classes (the grammar
  repeats the field per base, the generic probe kept one); a small class_base_names dispatches ST there
  and leaves extract_base_classes unchanged; find_class_body answers ST before the generic body probe, which
  would otherwise take a trailing body statement for the member container.
• extract_usages.c: declared VAR names bind (plural names field), a declaration's initial_value
  stays a read; that check and the existing type-field check now share one helper,
  is_non_binding_decl_field.

Credit: @ysfsmet for the ST groundwork and the discussion in #1810.

In scope / out of scope

• In: the grammar, language registration, count surfaces, definition/base/usage extraction, tests.
• Out (following PRs): vendor dialect normalization (1b), the export layout with members after
  END_FUNCTION_BLOCK (1c), the remaining real-world dialect (1d). Without them most real exports parse
  only partially (see the table: 86 % of the proof project's files at this stage).

Vendoring checklist

• internal/cbm/vendored/grammars/st/LICENSE (MIT, upstream text)
• THIRD_PARTY.md entry
• SBOM: generated dynamically from the vendored tree, nothing to edit
• internal/cbm/vendored/grammars/MANIFEST.md: paragraph + table row + recounted summary/ABI lines;
  "Vendored unmodified; vendor dialect is normalized in internal/cbm/st_dialect.c before parsing."
• scripts/vendored-checksums.txt regenerated; make -f Makefile.cbm security passes
• Count surfaces 162 -> 163: README, docs/index.html, docs/llms.txt, pkg/npm/README.md, chocolatey
  nuspec, scripts/package-release.sh, server.json. Four places that still read 158 at the base
  (README.md:229, docs/index.html:57 and :451, docs/llms.txt:8) are corrected too; the language-count
  contract regex does not cover them.
• Same wiring as the Chialisp precedent: LANG_NAME_TABLE in userconfig.c, a
  CBM_GRAMMAR_CASES fixture, a LABEL_GOLDENS row, lang_ext_st, call-node manifest and language
  registry repro rows (the manifest assert message now states the real count, 228).

Commits

1. feat(lang): add IEC 61131-3 Structured Text (.st)
2. feat(st): extract definitions, bases and usages from .st

Size

Production +141 / -8 (extract_defs.c +63 / -1, extract_usages.c +29 / -7, lang_specs.c +39,
registration +10), tests +249 / -11, docs and metadata +64 / -30 (including MANIFEST.md and
vendored-checksums.txt), vendored grammar +97,336 (generated parser.c and friends, excluded from review
size). Per commit: language +49 prod / +67 -11 test; extraction +92 / -8 prod, +182 test.

Checks

• Focused suites (extraction grammar_regression grammar_labels language lang_contract userconfig): all pass (602 PASS lines) except the known environment failure test_extraction.c: sp is NULL; the first commit alone builds and passes the same suites
• make test-repro: the same 11 suites / 15 tests fail as on main in this environment (issue480, 523, 546, ... - HTTP/network dependent); the ST repro rows pass
• scripts/lint.sh --ci: rc 0
• lint-tidy-diff (clang-tidy 21.1.6, diff against the prerequisite): one finding, in upstream code the
  change has to touch: is_binding_occurrence is over the cognitive-complexity threshold on main (33).
  This PR lowers it to 32 (the type-field check and the ST initial_value check now share
  is_non_binding_decl_field), but the diff-scoped run still reports the function because a changed line
  sits inside it. extract_base_classes is left byte-identical to main.

Proof on a real project

Stage	partial .st files	nodes	edges	index time, median (3 runs)
upstream main @ 64c23fa	.st not indexed	297	300	7.67 s (7.67 / 7.67 / 7.40)
1a language (4c7bc08)	822 / 956 (86.0 %)	3430	8320	8.65 s (8.43 / 8.93 / 8.65)
1b normalizer (bb6c46e)	263 / 956 (27.5 %)	3431	8153	7.94 s (7.94 / 7.94 / 7.93)
1c export layout (9ec9502)	156 / 956 (16.3 %)	5045	17550	7.94 s (7.94 / 7.92 / 8.18)
1d real-world (49e8e9c)	6 / 956 (0.6 %)	5108	17575	7.93 s (7.94 / 7.93 / 7.92)

Machine: Linux 6.18.33.2-microsoft-standard-WSL2 x86_64 (WSL2 on Windows 11), 13th Gen Intel Core i9-13950HX, 32 logical CPUs, 15 GiB RAM visible to WSL. Release CLI (make -f Makefile.cbm cbm, -O2), cli index_repository on SRCI @ 67fd773 (956 .st files), fresh CBM_CACHE_DIR and CBM_RUNTIME_DIR per run, median of 3 wall-clock runs, nothing else running. Wall time includes process start and the non-ST files; it stays flat because the ST files are small.

Edges by type, 1b -> 1c: CALLS 104 -> 4007, DEFINES_METHOD 2 -> 1606, USAGE 4512 -> 5803, WRITES 0 -> 460, OVERRIDE 0 -> 401. 1c -> 1d: DEFINES 3740 -> 3803 (types that parse now), USAGE 5803 -> 5765 (struct field names no longer read as usages). 1a -> 1b: edges 8320 -> 8153, of which USAGE 4681 -> 4512.

Known limitations (this stage)

• .st is also used by Pharo/Smalltalk Tonel (*.class.st) and StringTemplate; such files would be
  parsed as ST and yield little or nothing.
• Real vendor exports mostly parse partially until 1b-1d land (86 % partial on the proof project here).

Written with Claude Code (Anthropic) on behalf of @SarletteD, who reviewed and signs off every commit.

[github-actions]

Thanks for opening this — it has been seen, and it is queued.

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Current review status: working through a backlog. 0.9.1-rc.1 is out, so the release freeze that held reviews is over — but it left a large queue of open pull requests behind it, and we are reading through them oldest-first. The background is in discussion #1144.

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