refactor: deduplicate code across logger, validation, and launcher packages

[lpcox]

Summary

Addresses all 15 open duplicate-code issues by implementing 4 targeted refactorings and closing issues where patterns were already resolved.

Changes

1. formatLogLine helper (logger/common.go)

Centralizes the [timestamp] [level] [category] message log line format used identically by FileLogger.Log() and ServerFileLogger.Log().

2. Session-conditional logging (launcher/log_helpers.go)

Consolidates if sessionID != "" branches in logLaunchStart, logTimeoutError, and logLaunchSuccess using the existing sessionSuffix() helper consistently.

3. InvalidPattern + InvalidValue helpers (config/rules/rules.go)

New reusable helpers for pattern validation and constraint violations. Applied to 5 inline ValidationError constructions in validation_schema.go (container, mount, URL, entrypoint, domain).

4. SchemaValidationError helper (config/rules/rules.go)

New helper for custom schema validation failures. Applied to 8 inline constructions in validation.go with consistent message format.

Already resolved patterns (close only)

• [duplicate-code] Duplicate Code Pattern: Mutex-Protected Tag Mutation in DIFC Agent #1767 (DIFC tag mutation): modifyTag helper already exists in difc/agent.go
• [duplicate-code] Duplicate Code Pattern: Global Logger RWMutex Access Pattern #1768 (Global logger RWMutex): withGlobalLogger helper already exists in logger/global_helpers.go
• [duplicate-code] Duplicate Code Pattern: Logger Initialization Boilerplate #1766 (Logger init boilerplate): initLogger generic helper already exists in logger/common.go
• [duplicate-code] Duplicate Code Pattern: Authorization Header Extraction in auth.go and http_helpers.go #1813 (Auth header extraction): Already properly delegated to auth.header.go
• [duplicate-code] Duplicate Code Pattern: Log Level Dispatch Quad-Functions in Logger Package #1883 (Log level dispatch): Already optimized with logFuncs map + one-liner wrappers

Closes

#1882, #1824, #1810, #1766, #1768, #1885, #1811, #1825, #1767, #1883, #1826, #1812, #1884, #1813, #1827

[Copilot]

Pull request overview

Refactors several internal packages to remove repeated boilerplate by introducing small, reusable helpers (logger line formatting, launcher session-aware logging formatting, and config validation error constructors) to keep behavior consistent and reduce future churn.

Changes:

• Centralize file-based logger line formatting via a shared helper used by both FileLogger and ServerFileLogger.
• Reduce session-conditional branching in launcher logging helpers by composing log strings with sessionSuffix().
• Introduce reusable ValidationError constructors (InvalidPattern, InvalidValue, SchemaValidationError) and apply them across schema/pattern validation codepaths.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/logger/common.go	Adds shared formatLogLine helper to standardize file log output format.
internal/logger/file_logger.go	Switches FileLogger.Log() to use formatLogLine (removes duplicated formatting code).
internal/logger/server_file_logger.go	Switches ServerFileLogger.Log() to use formatLogLine (removes duplicated formatting code).
internal/launcher/log_helpers.go	Refactors launch/timeout/success logging to reduce sessionID != "" branching via sessionSuffix().
internal/config/rules/rules.go	Adds reusable ValidationError helper constructors for patterns/values/schema validation.
internal/config/validation_schema.go	Replaces inline ValidationError literals with InvalidPattern / InvalidValue.
internal/config/validation.go	Replaces inline ValidationError literals with SchemaValidationError / InvalidValue.

Comments suppressed due to low confidence (2)

internal/launcher/log_helpers.go:105

• The logLauncher.Printf message switched from explicitly logging sessionID=%s to appending sessionSuffix into serverID=%s%s. Since logLauncher also forwards to the file logger (LogDebug), dropping a dedicated sessionID= field makes filtering/grep’ing for a session harder and changes the log semantics. Prefer keeping serverID=%s and adding , sessionID=%s when sessionID != "" (possibly via a helper) rather than reusing the human-readable suffix.

	log.Printf("[LAUNCHER] ⚠️  The server may be hanging or taking too long to initialize")
	log.Printf("[LAUNCHER] ⚠️  Consider increasing 'startupTimeout' in gateway config if server needs more time")
	logLauncher.Printf("Startup timeout occurred: serverID=%s%s, timeout=%v", serverID, suffix, l.startupTimeout)

internal/launcher/log_helpers.go:113

• Same issue as timeout logging: logLauncher.Printf("Connection established: serverID=%s%s", ...) no longer logs sessionID as a distinct key/value when a session is present. Because these messages are also written to the file logger via Logger.Printf → LogDebug, keeping sessionID=%s explicitly is more useful for log searching and consistency with other launcher debug messages.

	suffix := sessionSuffix(sessionID)
	logger.LogInfoWithServer(serverID, "backend", "Successfully launched MCP backend server%s: server=%s%s", suffix, serverID, suffix)
	log.Printf("[LAUNCHER] Successfully launched: %s%s", serverID, suffix)
	logLauncher.Printf("Connection established: serverID=%s%s", serverID, suffix)

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