Fixes #158 - Setup copilot instructions (#226)

* Fixes #158 - Setup copilot instructions

* fix review comments

Author: vivganes

.github/copilot-instructions.md

@@ -0,0 +1,53 @@
+# GitHub Copilot SDK — Assistant Instructions
+
+**Quick purpose:** Help contributors and AI coding agents quickly understand this mono-repo and be productive (build, test, add SDK features, add E2E tests). ✅
+
+## Big picture 🔧
+
+- The repo implements language SDKs (Node/TS, Python, Go, .NET) that speak to the **Copilot CLI** via **JSON‑RPC** (see `README.md` and `nodejs/src/client.ts`).
+- Typical flow: your App → SDK client → JSON-RPC → Copilot CLI (server mode). The CLI must be installed or you can connect to an external CLI server via the `CLI URL option (language-specific casing)` (Node: `cliUrl`, Go: `CLIUrl`, .NET: `CliUrl`, Python: `cli_url`).
+
+## Most important files to read first 📚
+
+- Top-level: `README.md` (architecture + quick start)
+- Language entry points: `nodejs/src/client.ts`, `python/README.md`, `go/README.md`, `dotnet/README.md`
+- Test harness & E2E: `test/harness/*`, Python harness wrapper `python/e2e/testharness/proxy.py`
+- Schemas & type generation: `nodejs/scripts/generate-session-types.ts`
+- Session snapshots used by E2E: `test/snapshots/` (used by the replay proxy)
+
+## Developer workflows (commands you’ll use often) ▶️
+
+- Monorepo helpers: use `just` tasks from repo root:
+  - Install deps: `just install` (runs npm ci, uv pip install -e, go mod download, dotnet restore)
+  - Format all: `just format` | Lint all: `just lint` | Test all: `just test`
+- Per-language:
+  - Node: `cd nodejs && npm ci` → `npm test` (Vitest), `npm run generate:session-types` to regenerate session-event types
+  - Python: `cd python && uv pip install -e ".[dev]"` → `uv run pytest` (E2E tests use the test harness)
+  - Go: `cd go && go test ./...`
+  - .NET: `cd dotnet && dotnet test test/GitHub.Copilot.SDK.Test.csproj`
+
+## Testing & E2E tips ⚙️
+
+- E2E runs against a local **replaying CAPI proxy** (see `test/harness/server.ts`). Most language E2E harnesses spawn that server automatically (see `python/e2e/testharness/proxy.py`).
+- Tests rely on YAML snapshot exchanges under `test/snapshots/` — to add test scenarios, add or edit the appropriate YAML files and update tests.
+- The harness prints `Listening: http://...` — tests parse this URL to configure CLI or proxy.
+
+## Project-specific conventions & patterns ✅
+
+- Tools: each SDK has helper APIs to expose functions as tools; prefer the language's `DefineTool`/`@define_tool`/`AIFunctionFactory.Create` patterns (see language READMEs).
+- Infinite sessions are enabled by default and persist workspace state to `~/.copilot/session-state/{sessionId}`; compaction events are emitted (`session.compaction_start`, `session.compaction_complete`). See language READMEs for usage.
+- Streaming: when `streaming`/`Streaming=true` you receive delta events (`assistant.message_delta`, `assistant.reasoning_delta`) and final events (`assistant.message`, `assistant.reasoning`) — tests expect this behavior.
+- Type generation is centralized in `nodejs/scripts/generate-session-types.ts` and requires the `@github/copilot` schema to be present (often via `npm link` or installed package).
+
+## Integration & environment notes ⚠️
+
+- The SDK requires a Copilot CLI installation or an external server reachable via the `CLI URL option (language-specific casing)` (Node: `cliUrl`, Go: `CLIUrl`, .NET: `CliUrl`, Python: `cli_url`) or `COPILOT_CLI_PATH`.
+- Some scripts (typegen, formatting) call external tools: `gofmt`, `dotnet format`, `tsx` (available via npm), `quicktype`/`quicktype-core` (used by the Node typegen script), and `prettier` (provided as an npm devDependency). Most of these are available through the repo's package scripts or devDependencies—run `just install` (and `cd nodejs && npm ci`) to install them. Ensure the required tools are available in CI / developer machines.
+- Tests may assume `node >= 18`, `python >= 3.9`, platform differences handled (Windows uses `shell=True` for npx in harness).
+
+## Where to add new code or tests 🧭
+
+- SDK code: `nodejs/src`, `python/copilot`, `go`, `dotnet/src`
+- Unit tests: `nodejs/test`, `python/*`, `go/*`, `dotnet/test`
+- E2E tests: `*/e2e/` folders that use the shared replay proxy and `test/snapshots/`
+- Generated types: update schema in `@github/copilot` then run `cd nodejs && npm run generate:session-types` and commit generated files in `src/generated` or language generated location.