feat(ast/powershell): Support powershell for codegraph

[weburnit]

Summary

Adds first-class PowerShell indexing to CodeGraph for scripts and modules:

• Language support (powershell) — .ps1, .psm1, and .psd1 are detected and parsed.
• Tree-sitter grammar — vendors tree-sitter-powershell.wasm from tree-sitter-powershell@0.26.4 after ABI/runtime health check.
• Symbol extraction — functions, classes, class methods, class properties, enums, enum members, and module-level variables.
• Flow extraction — command calls, case-insensitive call resolution, using module, Import-Module, and dot-sourced script imports.

What Changed

12 files touched, including 1 vendored WASM grammar:

• src/types.ts — adds powershell to the Language union.
• src/extraction/grammars.ts — maps .ps1 / .psm1 / .psd1, loads the vendored PowerShell WASM, and adds the display name.
• src/extraction/languages/powershell.ts (new) — PowerShell extractor for functions, classes, members, enums, imports, command calls, and signatures.
• src/extraction/languages/index.ts — registers the PowerShell extractor.
• src/extraction/wasm/tree-sitter-powershell.wasm (new) — vendored ABI-15 tree-sitter grammar.
• src/extraction/tree-sitter.ts — handles PowerShell enum-member names, module-level assignments, class inheritance, and command/import extraction inside function bodies.
• src/resolution/import-resolver.ts — resolves PowerShell module/script imports to file nodes.
• src/resolution/name-matcher.ts — adds case-insensitive exact-name fallback for PowerShell commands and symbols.
• src/resolution/index.ts — lets the resolver pre-filter accept case-insensitive PowerShell matches.
• __tests__/extraction.test.ts — adds language detection, symbol extraction, and cross-file resolution coverage.
• README.md — documents PowerShell in supported languages.
• CHANGELOG.md — adds an [Unreleased] user-facing entry.

Why

PowerShell automation repos are often split across .psm1 modules, dot-sourced .ps1 helper scripts, and command-style function calls. Before this change, CodeGraph treated those files as unsupported, so agents had to fall back to file reads and grep to understand script/module flows.

This completes the static-processing path for common PowerShell projects: CodeGraph can now find PowerShell entry points, trace calls between functions, and surface module/script dependencies without reading every script by hand.

Design Decisions

Decision	Rationale
Vendor tree-sitter-powershell.wasm	tree-sitter-wasms does not ship PowerShell; the npm grammar ships a healthy ABI-15 WASM.
Support .ps1, .psm1, and .psd1	These are the core script, module, and manifest/data extensions PowerShell projects rely on.
Treat PowerShell calls as command AST nodes	PowerShell function invocation is command-shaped (Get-Thing -Name x), not conventional call_expression syntax.
Resolve command names case-insensitively	PowerShell command and function names are case-insensitive in normal execution.
Model using module, Import-Module, and dot-sourcing as imports	These are the static module/script loading forms that create cross-file dependencies.
Skip dynamic invocation guesses	Shapes like & $cmd or wildcard dot-sourcing are runtime-dynamic; missing an edge is safer than creating a wrong one.

Verification

✓ tree-sitter grammar health check → ABI 15, 20/20 clean parses
✓ npm run build → TypeScript build and asset copy pass
✓ npx vitest run __tests__/extraction.test.ts -t "PowerShell" → 3/3 PowerShell tests pass
✓ npx vitest run __tests__/extraction.test.ts → 375/375 extraction tests pass
✓ npm test → 1579 passed, 2 skipped
✓ sample PowerShell project verification → PASS, 2 files indexed, 13 nodes, 14 edges

Test Coverage

Test	Asserts
Language detection	.ps1, .psm1, and .psd1 detect as powershell; .ps1 is accepted as a source file.
Language support list	powershell appears in getSupportedLanguages().
Symbol extraction	Extracts function, class, method, property, enum, enum member, and module-level variable nodes.
Import extraction	Emits import references for using module / Import-Module static paths.
Command call extraction	Emits call references for command-style function invocations and nested script-block commands.
Inheritance extraction	Extracts PowerShell base classes from class Child : Base.
Cross-file resolution	Resolves using module ./Private/Helpers.psm1 to the helper module file.
Case-insensitive call resolution	Resolves find-widget to function Find-Widget.

Migration

None. PowerShell support is additive. No schema changes and no breaking changes.

Existing projects should re-index to pick up PowerShell files:

codegraph index -f

For a new PowerShell project:

codegraph init