docs: Add Copilot instructions

Author: nzakas

.github/copilot-instructions.md

@@ -0,0 +1,126 @@
+# Coding Guidelines
+
+## Indentation
+
+We use tabs, not spaces.
+
+## Naming Conventions
+
+- Use PascalCase for `type` names
+- Use camelCase for `function` and `method` names
+- Use camelCase for `property` names and `local variables`
+- Use whole words in names when possible
+
+## Comments
+
+- When there are comments for `functions`, `interfaces`, `enums`, and `classes` use JSDoc style comments
+
+## Strings
+
+- Use "double quotes" for strings
+
+## Style
+
+- Use arrow functions `=>` over anonymous function expressions
+- Only surround arrow function parameters when necessary. For example, `(x) => x + x` is wrong but the following are correct:
+
+```javascript
+x => x + x
+(x, y) => x + y
+<T>(x: T, y: T) => x === y
+```
+
+- Always surround loop and conditional bodies with curly braces
+- Open curly braces always go on the same line as whatever necessitates them
+- Parenthesized constructs should have no surrounding whitespace. A single space follows commas, colons, and semicolons in those constructs. For example:
+
+```javascript
+for (let i = 0, n = str.length; i < 10; i++) {
+    if (x < 10) {
+        foo();
+    }
+}
+
+function f(x: number, y: string): void { }
+```
+
+## OpenAI API
+
+For OpenAI API calls, we use the Responses API.
+
+Here's an example using CURL:
+
+```shell
+curl https://api.openai.com/v1/responses \
+  -H "Content-Type: application/json" \
+  -H "Authorization: Bearer $OPENAI_API_KEY" \
+  -d '{
+    "model": "gpt-4o-mini",
+    "instructions": "You are a mom of a three-year-old girl.",
+    "input": "Tell me a three sentence bedtime story about a unicorn.",
+    "previous_response_id": "resp_123456abcdef"
+  }'
+```
+
+We only use `previous_response_id` when we need to retry the request.
+
+And here's an example response:
+
+```json
+{
+	"id": "resp_67ccd2bed1ec8190b14f964abc0542670bb6a6b452d3795b",
+	"object": "response",
+	"created_at": 1741476542,
+	"status": "completed",
+	"error": null,
+	"incomplete_details": null,
+	"instructions": null,
+	"max_output_tokens": null,
+	"model": "gpt-4o-2024-08-06",
+	"output": [
+		{
+			"type": "message",
+			"id": "msg_67ccd2bf17f0819081ff3bb2cf6508e60bb6a6b452d3795b",
+			"status": "completed",
+			"role": "assistant",
+			"content": [
+				{
+					"type": "output_text",
+					"text": "In a peaceful grove beneath a silver moon, a unicorn named Lumina discovered a hidden pool that reflected the stars. As she dipped her horn into the water, the pool began to shimmer, revealing a pathway to a magical realm of endless night skies. Filled with wonder, Lumina whispered a wish for all who dream to find their own hidden magic, and as she glanced back, her hoofprints sparkled like stardust.",
+					"annotations": []
+				}
+			]
+		}
+	],
+	"parallel_tool_calls": true,
+	"previous_response_id": null,
+	"reasoning": {
+		"effort": null,
+		"summary": null
+	},
+	"store": true,
+	"temperature": 1.0,
+	"text": {
+		"format": {
+			"type": "text"
+		}
+	},
+	"tool_choice": "auto",
+	"tools": [],
+	"top_p": 1.0,
+	"truncation": "disabled",
+	"usage": {
+		"input_tokens": 36,
+		"input_tokens_details": {
+			"cached_tokens": 0
+		},
+		"output_tokens": 87,
+		"output_tokens_details": {
+			"reasoning_tokens": 0
+		},
+		"total_tokens": 123
+	},
+	"user": null,
+	"metadata": {}
+}
+```