debug: structured tool/HTTP logging, request IDs, config dump

Closes #13.

Today GITEA_DEBUG=true only flips the zap level to debug, dumps a
contextless `Text Result:` blob per tool call, and enables the gitea
SDK's own debug stream (which doesn't merge with our log file). That is
not enough to diagnose a misbehaving tool call in production.

This change introduces:

- A `pkg/middleware.ToolLogging` ToolHandlerMiddleware that logs each
  tool invocation on entry and exit with structured fields: tool name,
  redacted args, request_id, token source, duration_ms, and status. The
  request_id is stashed in the context so downstream layers can
  correlate.
- A `loggingRoundTripper` in `pkg/gitea` that wraps the shared HTTP
  transport and emits one structured line per upstream Gitea API call
  (method, token-stripped URL, status, duration_ms, bytes). This
  replaces — and is far more useful than — `gitea.SetDebugMode()`.
- An effective-config dump at startup (`logEffectiveConfig`) when
  debug+config scope is on, so "did my env var get picked up?" becomes
  answerable from the log file.
- Token source tracking. CLI flag / GITEA_ACCESS_TOKEN /
  GITEA_ACCESS_TOKEN_FILE / per-request Authorization header are now
  distinguished in logs as flag/env/env-file/header.
- A baseline redactor in `pkg/debug` that masks args / query params
  whose keys look like secrets (token, password, secret, api_key,
  authorization, …). This is the placeholder for issue #5's shared
  redactor; once that lands, callers here should defer to it.
- `GITEA_DEBUG_SCOPES` env var to scope debug output to any subset of
  `tools,http,config`. Default (unset) is "everything".

Test coverage was added for the redactor, scope flag, request-id
helpers, preview truncation (multibyte-safe), and the middleware's
context wiring + error propagation.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pkg/middleware/logging.go

@@ -0,0 +1,87 @@
+// Package middleware contains MCP tool-handler middlewares.
+package middleware
+
+import (
+	"context"
+	"time"
+
+	mcpContext "gitea.com/gitea/gitea-mcp/pkg/context"
+	"gitea.com/gitea/gitea-mcp/pkg/debug"
+	"gitea.com/gitea/gitea-mcp/pkg/flag"
+	"gitea.com/gitea/gitea-mcp/pkg/log"
+
+	"github.com/mark3labs/mcp-go/mcp"
+	"github.com/mark3labs/mcp-go/server"
+	"go.uber.org/zap"
+)
+
+// ToolLogging wraps a ToolHandlerFunc to emit structured entry/exit logs
+// for every tool invocation. When debug is off it is effectively a no-op
+// aside from attaching a request ID and tool name to the context (which the
+// `to` package and the HTTP RoundTripper read for correlation).
+//
+// At debug level we log:
+//   - on entry: tool name, redacted args, request_id, token source
+//   - on exit:  status (ok/error), duration_ms, error message if any
+//
+// At error level we always log a contextual error entry (even when debug is
+// off) so an operator looking at the log can tell *which* tool failed.
+func ToolLogging(next server.ToolHandlerFunc) server.ToolHandlerFunc {
+	return func(ctx context.Context, req mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+		reqID := debug.NewRequestID()
+		ctx = context.WithValue(ctx, mcpContext.RequestIDContextKey, reqID)
+		ctx = context.WithValue(ctx, mcpContext.ToolNameContextKey, req.Params.Name)
+
+		tokenSource := tokenSourceFromContext(ctx)
+
+		if flag.DebugScopeEnabled("tools") {
+			log.Debug("tool call: start",
+				zap.String("tool", req.Params.Name),
+				zap.String("request_id", reqID),
+				zap.String("token_source", tokenSource),
+				zap.Any("args", debug.RedactArgs(req.Params.Arguments)),
+			)
+		}
+
+		start := time.Now()
+		result, err := next(ctx, req)
+		duration := time.Since(start)
+
+		fields := []zap.Field{
+			zap.String("tool", req.Params.Name),
+			zap.String("request_id", reqID),
+			zap.Int64("duration_ms", duration.Milliseconds()),
+		}
+
+		switch {
+		case err != nil:
+			// Always-on contextual error log. This replaces the bare
+			// `log.Errorf("%s", err)` previously in pkg/to.ErrorResult,
+			// which had no tool name attached.
+			log.Error("tool call: error",
+				append(fields, zap.String("error", err.Error()))...)
+		case result != nil && result.IsError:
+			if flag.DebugScopeEnabled("tools") {
+				log.Debug("tool call: returned isError=true", fields...)
+			}
+		default:
+			if flag.DebugScopeEnabled("tools") {
+				log.Debug("tool call: ok", fields...)
+			}
+		}
+
+		return result, err
+	}
+}
+
+func tokenSourceFromContext(ctx context.Context) string {
+	if ctx != nil {
+		if v, ok := ctx.Value(mcpContext.TokenSourceContextKey).(string); ok && v != "" {
+			return v
+		}
+	}
+	if flag.TokenSource != "" {
+		return flag.TokenSource
+	}
+	return "none"
+}