add AGENTS.md, rename default branch to main

.github/workflows/test.yml

@@ -2,16 +2,16 @@ name: Test
 
 on:
   push:
-    branches: [master]
+    branches: [main]
   pull_request:
-    branches: [master]
+    branches: [main]
 
 jobs:
   test:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: ['1.20', '1.21', '1.22', '1.23']
+        go-version: ['1.21', '1.22', '1.23', '1.24']
 
     steps:
       - uses: actions/checkout@v4
@@ -29,3 +29,30 @@ jobs:
 
       - name: Run tests
         run: go test -v -race ./...
+
+  test-tip:
+    runs-on: ubuntu-latest
+    continue-on-error: true
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Go stable (for gotip bootstrap)
+        uses: actions/setup-go@v5
+        with:
+          go-version: stable
+
+      - name: Install gotip
+        run: |
+          go install golang.org/dl/gotip@latest
+          gotip download
+          echo "$(gotip env GOROOT)/bin" >> $GITHUB_PATH
+
+      - name: Verify formatting
+        run: test -z "$(gofmt -l .)"
+
+      - name: Run go vet
+        run: gotip vet ./...
+
+      - name: Run tests
+        run: gotip test -v -race ./...

AGENTS.md

@@ -0,0 +1,139 @@
+# AGENTS.md
+
+Guidelines for AI agents operating in the `simple-scrypt` repository.
+
+## Project overview
+
+Single-package Go library wrapping `golang.org/x/crypto/scrypt` for password hashing.
+Module path: `github.com/elithrar/simple-scrypt`. One external dependency (`golang.org/x/crypto`).
+
+Two source files at the repo root:
+- `scrypt.go` — library implementation (public API mirrors Go's `bcrypt` package)
+- `scrypt_test.go` — tests (standard `testing` package, no third-party frameworks)
+
+Hash format: `N$R$P$hexsalt$hexdk` (dollar-separated, hex-encoded salt and derived key).
+
+Default branch is **`main`**.
+
+## Build and test commands
+
+```sh
+# build
+go build ./...
+
+# run full test suite (CI uses this exact command)
+go test -v -race ./...
+
+# run a single test
+go test -v -race -run TestCompareHashAndPassword ./...
+
+# run a single sub-test (table-driven)
+go test -v -race -run TestCalibrate/512 ./...
+
+# formatting check — CI rejects any diff
+gofmt -l .
+
+# apply formatting fixes
+gofmt -w .
+
+# static analysis — CI runs this
+go vet ./...
+```
+
+CI runs on push/PR to `main` across Go 1.21, 1.22, 1.23, 1.24 plus tip on Ubuntu.
+All three checks must pass: `gofmt`, `go vet`, `go test -v -race ./...`.
+
+Always run `go test -v -race ./...` before committing to catch data races and regressions.
+
+## Code style
+
+### Formatting
+
+`gofmt` is the only formatter. No custom config. CI enforces zero diff — run `gofmt -w .` before committing.
+
+### Imports
+
+Standard library first, blank line, then external packages:
+
+```go
+import (
+    "crypto/rand"
+    "errors"
+    "fmt"
+
+    "golang.org/x/crypto/scrypt"
+)
+```
+
+### Naming
+
+- Exported types/functions: `PascalCase` — `Params`, `GenerateFromPassword`, `CompareHashAndPassword`
+- Unexported functions/constants: `camelCase` — `decodeHash`, `maxInt`, `minDKLen`
+- Sentinel errors: `Err` prefix — `ErrInvalidHash`, `ErrInvalidParams`, `ErrMismatchedHashAndPassword`
+- Receiver names: short, single letter — `p` for `*Params`
+
+### Error handling
+
+- Sentinel errors as package-level `var` using `errors.New()`
+- Functions return `error` as the last return value
+- Early return on error (guard clauses) — no nested else blocks
+- No error wrapping in this codebase; return sentinel errors or upstream errors directly
+- `CompareHashAndPassword` returns `nil` on success (bcrypt convention)
+
+```go
+var ErrInvalidHash = errors.New("scrypt: the provided hash is not in the correct format")
+
+func Cost(hash []byte) (Params, error) {
+    params, _, _, err := decodeHash(hash)
+    return params, err
+}
+```
+
+### Comments
+
+- Godoc comments on all exported types, functions, and variables
+- Internal comments explain *why*, not *what* — save them for I/O, validation, and edge cases
+- Don't comment single variables or trivial functions
+
+### Testing
+
+Standard `testing` package only. Tests are in `package scrypt` (white-box, same package).
+
+Patterns used in this codebase:
+
+- **Table-driven tests** with `pass bool` fields for expected outcomes:
+  ```go
+  var testParams = []struct {
+      pass   bool
+      params Params
+  }{
+      {true, Params{16384, 8, 1, 32, 64}},
+      {false, Params{-1, 8, 1, 16, 32}},
+  }
+  ```
+- `t.Fatal` / `t.Fatalf` for hard failures that should stop the test
+- `t.Errorf` for soft failures (test continues to check remaining cases)
+- `t.Logf` for informational output (e.g., timing data)
+- `Example*` functions for godoc examples
+
+Do not add third-party test frameworks or assertion libraries.
+Avoid tests that merely exercise language features — focus on validation, state, and error handling.
+
+### Types
+
+- Do not use type casts to work around type issues; fix the underlying problem
+- Zero-value structs (e.g., `Params{}`) are used as signals for default behavior (see `Calibrate`)
+
+## Dependencies
+
+Minimize new dependencies. The library has one external dependency by design.
+Install dependencies using `go get`. Ensure `go.sum` is committed alongside `go.mod` changes.
+
+## Git and PR conventions
+
+- Short, imperative commit messages: `add calibration benchmarks` not `feat(scrypt): added calibration benchmarks`
+- Do not commit, push, or create PRs without explicit instruction
+- Use `gh` CLI for creating PRs and issues
+- Branch off `main` for new work; never commit directly to `main`
+- PRs: short opening sentence with the "why", bullet points for major changes, mention related docs/tests
+- Do not list changed files in PR descriptions — the diff shows that