feat: PowerShell language support (.ps1/.psm1)

[qoole]

Builds on #40 (tree-sitter 0.25) — this branch is stacked on that PR's branch, so its two commits appear here until #40 merges; the PowerShell work is the five commits from chore: add PowerShell tree-sitter grammar onward. Opening as a draft until #40 lands, then I'll rebase onto main and mark it ready.

Tier-1 graph extraction for PowerShell via tree-sitter-powershell (airbus-cert; prebuilds for all six platform/arch combos — the reason #40's 0.25 runtime bump is the prerequisite).

What

• Definitions: functions (incl. filter/workflow), classes, methods & constructors, enums. exported=true for top-level defs and class members; functions nested inside functions/methods are scope-local → false. (PowerShell has no file-local export syntax; Export-ModuleMember/manifest interpretation is cross-file and deferred — see limitations.)
• Call edges: command invocations (scope-/module-qualifiers stripped: script:Foo, Mod\Get-Foo), member calls $obj.M(), static calls [Type]::M(), call-operator statics & Get-Foo. Dynamic invocation (& $var) produces no edge.
• Import edges: dot-sourcing (. ./x.ps1, quoted paths, backslash-normalized), Import-Module with relative paths (module names stay external specifiers, like Go stdlib imports), using module (extracted from its command shape — the grammar has no dedicated node).
• Case-insensitive resolution: PowerShell is case-insensitive; call/heritage/typed-member lookups case-fold within a PowerShell-only domain (a PS FOO can never link to a Python foo), original casing preserved everywhere, lookup order exact-local → folded-local → exact-global → folded-global (local scope wins, matching PS semantics). Folded matches surface as confidence: "inferred".
• Typed-receiver bindings: typed params (incl. decorated [Parameter(...)][Widget]$w), typed properties, cast declarations, [Widget]::new(), New-Object (positional and -TypeName), $this → enclosing class.
• Builtin-cmdlet denylist: calls to the core cmdlet/Pester-DSL surface (Get-ChildItem, Describe, …) never bind to a same-named in-repo definition (usually a Pester mock) — dropped-edge-is-safe, the same posture the resolver already takes for unresolvable member calls.
• Ingest: UTF-16LE .ps1 (Windows PowerShell 5.1 Out-File default) decoded at the shared readSourceFile site (hash-what-you-parse holds); Pester *.Tests.ps1 classified as test files and de-ranked accordingly; .psd1 deliberately not graph-parsed (manifests yield no definitions).
• Deep grammar import (tree-sitter-powershell/bindings/node/index.js) avoids a DEP0151 warning on every CLI run (package has extensionless main + no exports map).

Fit with recent main

This was originally built against pre-0.9.0 main and re-anchored after the recent landings; the seams were adapted rather than ported blind:

• Language-vs-parser reporting (Two small accuracy fixes: build banner under-reports indexed languages; README overstates what init writes for Claude Code #36): PowerShell slots into the EXTENSIONS table as two rows (.ps1/.psm1 → grammar powershell, label powershell), so the banner/map coverage report is correct by construction.
• Imported-function references (callers misses consumers that reference a function without calling it directly #34): the "don't descend into import statements" rule gets one PS carve-out — a dot-source can wrap a whole script block (. { ... }), whose body must still be walked for its own calls. Pinned by test.
• Strict member-call resolution (map clusters one entry per file instead of per directory #35): PS member calls inherit the drop-don't-guess rule unchanged; the PS case-folding applies inside resolveTypedMember's owner-qualified lookup, never as a bare-name fallback.
• Gitignore-aware walker / posix paths / UTF-16 read coherence / encoding-drift: PS files flow through the same enumeration, path storage, and readSourceFile contracts as every other language — no PS-specific read or walk path exists.

Evidence

• Suite: 618/618 green on this branch (35 PowerShell-specific tests: full-pipeline fixtures modeled on the Go tests, bindings, case-collision isolation, malformed-input tolerance, UTF-16, CRLF, >32 KB files, parser alternation, test-path classification pinning).
• Real-world battery (run on the pre-rebase branch; spot-revalidated post-rebase): 8 repos (Pester, ComputerManagementDsc, dbatools, ImportExcel, posh-git, PSFramework, Plaster, psake) — every build clean, double-build byte-identical determinism 8/8, incremental rebuild correct 8/8 (dbatools: 1,707 files, full 34 s / incremental 2.5 s).
• Function recall vs an exhaustive regex census: 88–98% per repo, with every miss attributed to upstream grammar parse errors, none to extraction logic.
• Resolution quality on dbatools: the most-called function (Stop-Function, 2,857 call sites, shadowed by 10 Pester mocks) resolves 726 incoming call edges to its production definition.
• Import wiring on posh-git: 24/30 import edges resolve to in-repo files via literal $PSScriptRoot resolution (was 0/30); the 6 unresolved are genuinely dynamic (runtime variables) and stay raw by design. Re-verified on this exact branch post-rebase, including byte-identical cold-rebuild determinism.
• Parse health (upstream grammar, not this integration): 41–94% of files parse error-free per repo; the dominant causes bisect to two airbus-cert grammar gaps (unquoted comma-separated bareword arguments; bare trailing scriptblock arguments). Extraction degrades gracefully — error-containing files still yield correct nodes and edges. Happy to file those upstream grammar issues.

Known limitations (deliberate)

• Export-ModuleMember / manifest FunctionsToExport not interpreted (uniform exported=true instead) — the common unquoted multi-name idiom doesn't parse in the current grammar anyway.
• $PSScriptRoot-interpolated, Join-Path-computed, and wildcard import arguments degrade to raw specifiers.
• .psd1 manifest relationships (RootModule/NestedModules) not graphed.
• Monorepo scope markers unchanged (PS has no fixed-name manifest file).
• Class base lists conflate base class and interfaces as extends (PS cannot define interfaces; targets stay external names).

[qoole]

Added a domain-isolation fix found while extending the language work: PowerShell method nodes were entering the shared member-owner index, so a typed member call from another language could in principle wire cross-language to a PS class method. PS methods (and PS heritage edges) now live only in their own indexes, mirroring how PS bare names were already isolated. Suite is 621/621 on the branch.