[log] log(envutil): add debug logging to env var parse fallbacks (#3825)

## Summary

Adds debug logging to `internal/envutil/envutil.go` to surface
misconfiguration earlier.

## What changed

Added `var logEnvUtil = logger.New("envutil:envutil")` and three
targeted `logEnvUtil.Printf` calls — one in each type-converting
function — that fire only when an environment variable is **set but
unusable**:

| Function | Log condition |
|---|---|
| `GetEnvInt` | Value is set but not a valid positive integer |
| `GetEnvDuration` | Value is set but not a valid positive duration |
| `GetEnvBool` | Value is set but not a recognised boolean
(`1/true/yes/on` / `0/false/no/off`) |

The `GetEnvString` function is intentionally not logged — it has no
parse step and adding a log there would be too noisy.

## Why

When an operator sets e.g. `MCP_GATEWAY_PAYLOAD_SIZE_THRESHOLD=512k` (an
invalid integer), the gateway silently falls back to the default with no
indication of what happened. With this change, enabling
`DEBUG=envutil:*` reveals the problem immediately:

```
envutil:envutil GetEnvInt: MCP_GATEWAY_PAYLOAD_SIZE_THRESHOLD="512k" is not a valid positive integer, using default=524288
```

## Quality checklist

- [x] Exactly 1 file modified
- [x] No test files modified
- [x] Logger declaration added (`var logEnvUtil =
logger.New("envutil:envutil")`)
- [x] Logger naming follows `pkg:filename` convention (matches
`logGitHub`/`logExpand` in the same package)
- [x] Logger arguments use only in-scope variables — no side effects
- [x] Log messages are meaningful and actionable
- [x] No duplication of existing logs
- [x] Import statements follow Go formatting conventions




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· ● 4.8M ·
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Author: lpcox

internal/envutil/envutil.go

@@ -5,8 +5,13 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	"github.com/github/gh-aw-mcpg/internal/logger"
+	"github.com/github/gh-aw-mcpg/internal/logger/sanitize"
 )
 
+var logEnvUtil = logger.New("envutil:envutil")
+
 // GetEnvString returns the value of the environment variable specified by envKey.
 // If the environment variable is not set or is empty, it returns the defaultValue.
 func GetEnvString(envKey, defaultValue string) string {
@@ -25,18 +30,21 @@ func GetEnvInt(envKey string, defaultValue int) int {
 		if value, err := strconv.Atoi(envValue); err == nil && value > 0 {
 			return value
 		}
+		logEnvUtil.Printf("GetEnvInt: %s=%q is not a valid positive integer, using default=%d", envKey, sanitize.TruncateSecret(envValue), defaultValue)
 	}
 	return defaultValue
 }
 
 // GetEnvDuration returns the time.Duration value of the environment variable specified by envKey.
-// If the environment variable is not set, is empty, or cannot be parsed by time.ParseDuration,
-// it returns the defaultValue. Accepts any string valid for time.ParseDuration (e.g. "2h", "30m", "90s").
+// If the environment variable is not set, is empty, cannot be parsed by time.ParseDuration,
+// or is not positive (> 0), it returns the defaultValue.
+// Accepts any string valid for time.ParseDuration (e.g. "2h", "30m", "90s").
 func GetEnvDuration(envKey string, defaultValue time.Duration) time.Duration {
 	if envValue := os.Getenv(envKey); envValue != "" {
 		if d, err := time.ParseDuration(envValue); err == nil && d > 0 {
 			return d
 		}
+		logEnvUtil.Printf("GetEnvDuration: %s=%q is not a valid positive duration, using default=%v", envKey, sanitize.TruncateSecret(envValue), defaultValue)
 	}
 	return defaultValue
 }
@@ -54,6 +62,7 @@ func GetEnvBool(envKey string, defaultValue bool) bool {
 		case "0", "false", "no", "off":
 			return false
 		}
+		logEnvUtil.Printf("GetEnvBool: %s=%q is not a recognized boolean value, using default=%v", envKey, sanitize.TruncateSecret(envValue), defaultValue)
 	}
 	return defaultValue
 }