feat: migrate configuration get to TypeScript

TS_MIGRATION_PLAN.md

@@ -0,0 +1,62 @@
+# TS_MIGRATION_PLAN.md
+
+This document describes a plan to migrate the Posit Publisher extension from
+using its current Go REST API `/configurations/${encodedName}` backend to an
+in-process TypeScript core package for loading a configuration.
+
+## Current State
+
+The `get` method in extensions/vscode/src/api/resources/Configurations.ts
+returns a `Promise` wrapping an `AxiosResponse` wrapping the domain types
+`Configuration | ConfigurationErrror` which are defined in
+extensions/vscode/src/api/types/configurations.ts.
+
+The callsite in extensions/vscode/src/state.ts uses the `data` field of the
+response.
+
+Errors are handled by a `catch` block that checks for Axios errors and handle
+them.
+
+## Desired End State
+
+The callsite in extensions/vscode/src/state.ts calls a pure-TypeScript function
+with no dependencies on vscode or axios. The `core` module defines an interface,
+`ConfigurationStore`, with a `get` function that matches the api resource
+function, but without the `AxiosResponse` wrapper. The `adapters` module defines
+`FSConfigurationStore`, an implementation of the interface that uses the
+`smol-toml` library to load and parse configurations from the file system. The
+callsite in state.ts handles potential errors from the TypeScript function.
+
+## Package Structure
+
+This is a suggested package structure.
+
+Key details:
+
+- the existing `api` types are maintained in-place to minimize changes during
+  the migration
+- `core` defines pure domain types, interfaces, and functions, with no
+  dependencies
+- `adapters` defines an implementation with dependencies on external packages
+  and the file system
+
+```
+extensions/vscode/
+├── adapters/
+│   └── fs-configuration-store.ts                 # ConfigurationStore → TOML files
+├── core/
+│   ├── ports.ts                                  # ConfigurationStore interface
+│   ├── errors.ts                                 # Domain errors and error helpers
+│   └── [other file names].ts                     # Pure domain functions (ported from Go)
+├── src/
+│   ├── state.ts                                  # Existing callsite uses new ConfigurationStore impl
+```
+
+## Approach
+
+Implement the TypeScript replacement as outlined, but stop and ask questions if
+anything doesn't make sense or requires deviating from the plan. Add tests for
+new code. Do not modify any go code. Make sure the extension continues to build
+and tests pass using the recipes in `extensions/vscode/justfile`. If you find
+yourself having to make a lot of changes to a lot of files, stop and ask for
+guidance. This should be a minimally invasive refactor.

extensions/vscode/package.json

@@ -680,6 +680,8 @@
   },
   "dependencies": {
     "@vscode/codicons": "^0.0.44",
+    "ajv": "^8.18.0",
+    "ajv-formats": "^3.0.1",
     "async-mutex": "^0.5.0",
     "axios": "^1.13.5",
     "debounce": "^3.0.0",
@@ -688,6 +690,7 @@
     "filenamify": "^7.0.1",
     "get-port": "^7.1.0",
     "retry": "^0.13.1",
+    "smol-toml": "^1.6.0",
     "tar-stream": "^3.1.7",
     "vscode-uri": "^3.0.8"
   }