Rename kit/ to rules/

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

rules/patterns/go-logging/contract.md

@@ -0,0 +1,64 @@
+# Contract: Logging (Go Web Applications)
+
+## Core Rule
+
+**All logging goes to the server binary's stdout/stderr — never to the browser console.**
+
+- `console.log`, `console.error`, `console.warn` in JavaScript are for debugging only.
+  Remove them before committing. They are not a substitute for server-side logging.
+- Diagnostic information (errors, slow queries, ingest results, background task status) must be
+  logged server-side so it is visible in the terminal where the binary runs.
+
+## Go Logging Standard
+
+Use the standard library `log/slog` (Go 1.21+) or `log` for simpler projects.
+
+```go
+// correct — structured, visible in binary console
+slog.Info("export started", "user", userID, "rows", count)
+slog.Error("db query failed", "err", err)
+
+// wrong — goes to browser devtools, invisible in production
+// (JS template rendered in HTML)
+// console.log("export started")
+```
+
+## Log Levels
+
+| Level   | When to use |
+|---------|-------------|
+| `Debug` | Detailed flow tracing; disabled in production builds |
+| `Info`  | Normal operation milestones: server start, request handled, export done |
+| `Warn`  | Recoverable anomaly: retry, fallback used, deprecated path |
+| `Error` | Operation failed; always include `"err", err` as a structured attribute |
+
+## What to Always Log
+
+- Server startup: address, port, config source.
+- Background task start/finish/error with task name and duration.
+- CSV/file export: scope, row count, duration.
+- Ingest/import: file name, rows accepted, rows rejected, error summary.
+- Any `500` response: handler name + error.
+
+## What Not to Log
+
+- Do not log full request bodies or CSV content — can contain PII or large payloads.
+- Do not log passwords, tokens, or secrets even partially.
+- Do not add `fmt.Println` for debugging and leave it in committed code.
+
+## htmx / Browser-rendered Responses
+
+- Handler errors that result in an htmx partial re-render must still log the error server-side.
+- Do not rely on the browser network tab as the only visibility into server errors.
+
+## Format
+
+- Use structured key-value attributes, not concatenated strings.
+
+```go
+// correct
+slog.Error("sync failed", "component", comp.Serial, "err", err)
+
+// wrong — hard to grep, hard to parse
+log.Printf("sync failed for component %s: %v", comp.Serial, err)
+```