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_test.go

@@ -0,0 +1,91 @@
+package middleware
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	mcpContext "gitea.com/gitea/gitea-mcp/pkg/context"
+	"gitea.com/gitea/gitea-mcp/pkg/debug"
+	"gitea.com/gitea/gitea-mcp/pkg/flag"
+
+	"github.com/mark3labs/mcp-go/mcp"
+)
+
+func TestToolLogging_PropagatesContextValues(t *testing.T) {
+	origDebug := flag.Debug
+	defer func() { flag.Debug = origDebug }()
+	flag.Debug = false // exercise the no-log code path; context wiring runs regardless
+
+	var (
+		gotToolName string
+		gotReqID    string
+	)
+	handler := func(ctx context.Context, _ mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+		gotToolName = debug.ToolNameFromContext(ctx)
+		gotReqID = debug.RequestIDFromContext(ctx)
+		return mcp.NewToolResultText("ok"), nil
+	}
+
+	wrapped := ToolLogging(handler)
+
+	req := mcp.CallToolRequest{}
+	req.Params.Name = "get_me"
+	req.Params.Arguments = map[string]any{"x": 1}
+
+	res, err := wrapped(context.Background(), req)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if res == nil {
+		t.Fatal("expected non-nil result")
+	}
+	if gotToolName != "get_me" {
+		t.Fatalf("tool name not propagated, got %q", gotToolName)
+	}
+	if gotReqID == "" {
+		t.Fatal("request id not propagated")
+	}
+}
+
+func TestToolLogging_ReturnsHandlerError(t *testing.T) {
+	want := errors.New("boom")
+	wrapped := ToolLogging(func(_ context.Context, _ mcp.CallToolRequest) (*mcp.CallToolResult, error) {
+		return nil, want
+	})
+
+	req := mcp.CallToolRequest{}
+	req.Params.Name = "broken_tool"
+
+	_, err := wrapped(context.Background(), req)
+	if !errors.Is(err, want) {
+		t.Fatalf("error not surfaced, got %v", err)
+	}
+}
+
+func TestTokenSourceFromContext(t *testing.T) {
+	origFlag := flag.TokenSource
+	defer func() { flag.TokenSource = origFlag }()
+
+	t.Run("falls back to flag.TokenSource", func(t *testing.T) {
+		flag.TokenSource = "env"
+		if got := tokenSourceFromContext(context.Background()); got != "env" {
+			t.Fatalf("got %q want env", got)
+		}
+	})
+
+	t.Run("returns none when no source is known", func(t *testing.T) {
+		flag.TokenSource = ""
+		if got := tokenSourceFromContext(context.Background()); got != "none" {
+			t.Fatalf("got %q want none", got)
+		}
+	})
+
+	t.Run("context value beats flag", func(t *testing.T) {
+		flag.TokenSource = "env"
+		ctx := context.WithValue(context.Background(), mcpContext.TokenSourceContextKey, "header")
+		if got := tokenSourceFromContext(ctx); got != "header" {
+			t.Fatalf("got %q want header", got)
+		}
+	})
+}