chore(ci): add copilot instructions (#4933)

General and Go-specific instructions for Copilot

.github/instructions/go.copilot-instructions.md

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+---
+applyTo: '**/*.go,**/go.mod,**/go.sum'
+description: 'Instructions for writing Go code following idiomatic Go practices and community standards'
+
+---
+
+# Go Development Instructions
+
+
+Follow idiomatic Go practices and community standards when writing Go code. These instructions are based on [Effective Go](https://go.dev/doc/effective_go), [Go Code Review Comments](https://go.dev/wiki/CodeReviewComments), and [Google's Go Style Guide](https://google.github.io/styleguide/go/guide).
+
+Refer to the linter configuration in `.golangci.yml` for style checks and standards
+
+## General Instructions
+
+- Write simple, clear, and idiomatic Go code
+- Favor clarity and simplicity over cleverness
+- Follow the principle of least surprise
+- Keep the non-error path left-aligned (minimize indentation)
+- Return early to reduce nesting
+- Prefer early return over if-else chains; use `if condition { return }` pattern to avoid else blocks
+- Make the zero value useful
+- Write self-documenting code with clear, descriptive names
+- Document exported types, functions, methods, and packages
+- Use Go modules for dependency management
+- Leverage and prefer the Go standard library when functionality exists instead of writing custom implementations (e.g., use `strings.Builder` for string concatenation, `filepath.Join` for path construction)
+- Write comments in English
+- Use allowed ASCII for identifiers; avoid using non-ASCII characters in identifiers
+- Avoid using emoji in code and comments
+
+## Naming Conventions
+
+### Packages
+
+- Use lowercase, single-word package names
+- Avoid underscores, hyphens, or mixedCaps
+- Choose names that describe what the package provides, not what it contains
+- Avoid generic names like `util`, `common`, or `base`
+
+#### Package Declaration Rules (CRITICAL):
+- **NEVER duplicate `package` declarations** - each Go file must have exactly ONE `package` line
+- When editing an existing `.go` file:
+  - **PRESERVE** the existing `package` declaration - do not add another one
+  - If you need to replace the entire file content, start with the existing package name
+- When creating a new `.go` file:
+  - **BEFORE writing any code**, check what package name other `.go` files in the same directory use
+  - Use the SAME package name as existing files in that directory
+  - If it's a new directory, use the directory name as the package name
+  - Write **exactly one** `package <name>` line at the very top of the file
+- When using file creation or replacement tools:
+  - **ALWAYS verify** the target file doesn't already have a `package` declaration before adding one
+  - If replacing file content, include only ONE `package` declaration in the new content
+  - **NEVER** create files with multiple `package` lines or duplicate declarations
+
+### Variables and Functions
+
+- Use mixedCaps or MixedCaps (camelCase) rather than underscores
+- Keep names short but descriptive
+- Use single-letter variables only for very short scopes (like loop indices)
+- Exported names start with a capital letter
+- Unexported names start with a lowercase letter
+- Avoid using the same name for the package and a type, (e.g., avoid `http.HTTPServer`, prefer `http.Server`)
+
+### Interfaces
+
+- Name interfaces with -er suffix when possible (e.g., `Reader`, `Writer`, `Formatter`)
+- Single-method interfaces should be named after the method (e.g., `Read` → `Reader`)
+- Keep interfaces small and focused
+
+### Constants
+
+- Use MixedCaps for exported constants
+- Use mixedCaps for unexported constants
+- Group related constants using `const` blocks
+- Consider using typed constants for better type safety
+
+## Code Style and Formatting
+
+### Formatting
+
+- Use `gofumt` to format code
+- Use `goimports` to manage ordering of `import` statements
+- Keep line length reasonable (no hard limit, but consider readability)
+- Add blank lines to separate logical groups of code, adhering to the linter constraints.
+
+### Comments
+
+- Strive for self-documenting code; prefer clear variable names, function names, and code structure over comments
+- Write comments only when necessary to explain complex implementation or non-obvious behavior
+- Write comments in complete sentences in English
+- Start sentences with the name of the item being described
+- Package comments should start with "Package [name]"
+- Use line comments (`//`) for most comments
+- Document the meaning of structs, interfaces and fields and their use.
+- Document the invariants expected when calling a function, the change of state
+  if any, and the expected state invariant when a function returns.
+- Document the rationale (why) and not how it is done, unless the implementation is complex
+
+## Architecture and Project Structure
+
+### Package Organization
+
+- Follow standard Go project layout conventions
+- Use `internal/` for packages that shouldn't be imported by external projects
+- Group related functionality into packages
+- Avoid circular dependencies
+- Put reusable packages in `internal/` if possible
+
+### Dependency Management
+
+- Use Go modules (`go.mod` and `go.sum`)
+- Keep dependencies minimal
+- Regularly update dependencies for security patches
+- Use `go mod tidy` to clean up unused dependencies
+
+## Type Safety and Language Features
+
+### Type Definitions
+
+- Define types to add meaning and type safety
+- Use struct tags for JSON, XML, database mappings
+- Use lower camelCase for field names in JSON tags
+- Prefer explicit type conversions
+- Use type assertions carefully and check whether the assertion succeeds using the second return value
+- Prefer generics over unconstrained types; when an unconstrained type is truly needed, use the predeclared alias `any` instead of `interface{}`
+
+### Pointers vs Values Parameter
+
+- Use pointer receivers for large structs or when you need to modify the receiver
+- Use value receivers for small structs and when immutability is desired
+- Use pointer parameters when you need to modify the argument or for large structs
+- Use value parameters for small structs and when you want to prevent modification
+- Be consistent with the receiver type, either use pointer receivers or value receivers for a given receiver type
+- Consider the zero value when choosing pointer vs value receivers
+
+### Interfaces and Composition
+
+- Accept interfaces, return concrete types
+- Keep interfaces small (1-3 methods is ideal)
+- Use embedding for composition
+- Define interfaces close to where they're used, not where they're implemented
+- Don't export interfaces unless necessary
+
+## Concurrency
+
+### Goroutines
+
+- Avoid creating goroutines in libraries; prefer letting the caller control concurrency
+- If you must create goroutines in libraries, provide clear documentation and cleanup mechanisms
+- Always know how a goroutine will exit
+- Use `sync.WaitGroup` or channels to wait for goroutines
+- Avoid goroutine leaks by ensuring cleanup
+
+### Channels
+
+- Use channels to communicate between goroutines
+- Don't communicate by sharing memory; share memory by communicating
+- Close channels from the sender side, not the receiver
+- Use buffered channels when you know the capacity
+- Use `select` for non-blocking operations
+
+### Synchronization
+
+- Use `sync.Mutex` for protecting shared state
+- Keep critical sections small
+- Use `sync.RWMutex` when you have many readers
+- Choose between channels and mutexes based on the use case: use channels for communication, mutexes for protecting state
+- Use `sync.Once` for one-time initialization
+
+## Error Handling Patterns
+
+### Creating Errors
+
+- Use `errors.New` for simple static errors (constant-like error values)
+- Create custom error types for domain-specific errors
+- Export error variables for sentinel errors
+- Use `errors.Is` and `errors.As` for error checking
+
+### Error Propagation
+
+- Add context when propagating errors up the stack
+- Use descriptive error messages with relevant context fields
+- Don't log and return errors (choose one)
+- Handle errors at the appropriate level
+- Use structured errors with fields for better debugging and monitoring
+
+### Error Handling
+
+- Check errors immediately after the function call
+- Don't ignore errors using `_` unless you have a valid reason (explain and document why)
+- Preserve error chains to maintain full context, wrap errors with context using `errors.Wrap()`
+
+- Create custom error types when checking for specific errors is needed
+- Place error returns as the last return value
+- Name error variables `err`
+- Keep error messages lowercase and don't end with punctuation
+
+### Error Lists and Multiple Errors
+
+- Use `errors.Join()` for collecting multiple errors (nil-safe)
+- Handle validation scenarios with error accumulation
+
+## API Design
+
+### JSON APIs
+
+- Use struct tags to control JSON marshaling
+- Validate input data
+- Use pointers for optional fields
+- Consider using `json.RawMessage` for delayed parsing
+- Handle JSON errors appropriately
+
+## Performance Optimization
+
+### Memory Management
+
+- Minimize allocations in hot paths
+- Reuse objects when a large number of those are allocated (consider `sync.Pool`)
+- Use value receivers for small structs
+- Preallocate slices when size is known
+- Avoid unnecessary string-byte conversions
+
+### I/O: Readers and Buffers
+
+- Most `io.Reader` streams are consumable once; reading advances state. Do not assume a reader can be re-read without special handling
+- If you must read data multiple times, buffer it once and recreate readers on demand:
+	- Use `io.ReadAll` (or a limited read) to obtain `[]byte`, then create fresh readers via `bytes.NewReader(buf)` or `bytes.NewBuffer(buf)` for each reuse
+	- For strings, use `strings.NewReader(s)`; you can `Seek(0, io.SeekStart)` on `*bytes.Reader` to rewind
+- For HTTP requests, do not reuse a consumed `req.Body`. Instead:
+	- Keep the original payload as `[]byte` and set `req.Body = io.NopCloser(bytes.NewReader(buf))` before each send
+	- Prefer configuring `req.GetBody` so the transport can recreate the body for redirects/retries: `req.GetBody = func() (io.ReadCloser, error) { return io.NopCloser(bytes.NewReader(buf)), nil }`
+- To duplicate a stream while reading, use `io.TeeReader` (copy to a buffer while passing through) or write to multiple sinks with `io.MultiWriter`
+- Reusing buffered readers: call `(*bufio.Reader).Reset(r)` to attach to a new underlying reader; do not expect it to “rewind” unless the source supports seeking
+- For large payloads, avoid unbounded buffering; consider streaming, `io.LimitReader`, or on-disk temporary storage to control memory
+
+- Use `io.Pipe` to stream without buffering the whole payload:
+	- Write to `*io.PipeWriter` in a separate goroutine while the reader consumes
+	- Always close the writer; use `CloseWithError(err)` on failures
+	- `io.Pipe` is for streaming, not rewinding or making readers reusable
+
+- **Warning:** When using `io.Pipe` (especially with multipart writers), all writes must be performed in strict, sequential order. Do not write concurrently or out of order—multipart boundaries and chunk order must be preserved. Out-of-order or parallel writes can corrupt the stream and result in errors.
+
+- Streaming multipart/form-data with `io.Pipe`:
+	- `pr, pw := io.Pipe()`; `mw := multipart.NewWriter(pw)`; use `pr` as the HTTP request body
+	- Set `Content-Type` to `mw.FormDataContentType()`
+	- In a goroutine: write all parts to `mw` in the correct order; on error `pw.CloseWithError(err)`; on success `mw.Close()` then `pw.Close()`
+	- Do not store request/in-flight form state on a long-lived client; build per call
+	- Streamed bodies are not rewindable; for retries/redirects, buffer small payloads or provide `GetBody`
+
+
+### Profiling
+
+- Use built-in profiling tools (`pprof`)
+- Benchmark critical code paths
+- Profile before optimizing
+- Focus on algorithmic improvements first
+- Consider using `testing.B` for benchmarks
+
+## Testing
+
+### Test Organization
+
+- Keep tests in the same package (white-box testing)
+- Use `_test` package suffix for black-box testing
+- Name test files with `_test.go` suffix
+- Place test files next to the code they test
+
+### Writing Tests
+
+- Use table-driven tests for multiple test cases
+- Name tests descriptively using `Test_functionName_scenario`
+- Use subtests with `t.Run` for better organization
+- Test both success and error cases
+- Have separate top-level tests for the success and error cases
+- Use `stretchr/testify/require` package for checking expected results
+
+### Test Helpers
+
+- Mark helper functions with `t.Helper()`
+- Create test fixtures for complex setup
+- Use `testing.TB` interface for functions used in tests and benchmarks
+- Clean up resources using `t.Cleanup()`
+
+## Security Best Practices
+
+### Input Validation
+
+- Validate all external input
+- Use strong typing to prevent invalid states
+- Sanitize data before using in SQL queries
+- Be careful with file paths from user input
+- Validate and escape data for different contexts (HTML, SQL, shell)
+
+### Cryptography
+
+- Use standard library crypto packages
+- Use crypto/rand for random number generation
+- Use TLS for network communication
+- Never store plain-text passwords
+- Store password hashes using functions designed for password hashing, such as PBKDF2 and scrypt
+
+## Documentation
+
+### Code Documentation
+
+- Prioritize self-documenting code through clear naming and structure
+- Document all exported symbols with clear, concise explanations
+- Start documentation with the symbol name
+- Write documentation in English
+- Use examples in documentation when helpful
+- Keep documentation close to code
+- Update documentation when code changes
+- Avoid emoji in documentation and comments
+
+### README and Documentation Files
+
+- Include clear setup instructions
+- Document dependencies and requirements
+- Provide usage examples
+- Document configuration options
+- Include troubleshooting section
+
+## Tools and Development Workflow
+
+### Essential Tools
+
+- `golangci-lint`: Primary linter
+- `go vet`: Find suspicious constructs
+- `go test`: Run tests
+- `go mod`: Manage dependencies
+- `go generate`: Code generation
+
+### Development Practices
+
+- Run tests before committing
+- Keep commits focused and atomic
+- Write meaningful commit messages
+- Review diffs before committing
+
+## Common Pitfalls to Avoid
+
+- Not checking errors
+- Ignoring race conditions
+- Creating goroutine leaks
+- Not using defer for cleanup
+- Modifying maps concurrently
+- Not understanding nil interfaces vs nil pointers
+- Forgetting to close or release resources (files, connections)
+- Using global variables unnecessarily
+- Over-using unconstrained types (e.g., `any`); prefer specific types or generic type parameters with constraints. If an unconstrained type is required, use `any` rather than `interface{}`
+- Not considering the zero value of types
+- **Creating duplicate `package` declarations** - this is a compile error; always check existing files before adding package declarations