Refactor: Remove authentication wrapper, clarify version management, document error types

[Copilot]

Semantic function clustering analysis identified 351 symbols across 27 clusters, revealing duplicate authentication logic and naming ambiguity in version management.

Changes

Remove authentication wrapper layer

• Deleted guard.ExtractAgentIDFromAuthHeader() - simple passthrough to auth.ExtractAgentID()
• Updated call sites to use auth package directly

// Before
agentID := guard.ExtractAgentIDFromAuthHeader(authHeader)

// After  
agentID := auth.ExtractAgentID(authHeader)

Disambiguate version setters

• config.SetVersion() → config.SetGatewayVersion() distinguishes from cmd.SetVersion()

Document error types

• Added godoc to ValidationError, EnvValidationResult, ViolationError explaining fields, usage patterns, and DIFC violation semantics

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• go.googlesource.com
  • Triggering command: /update-job-proxy /update-job-proxy /internal/difc /home/REDACTED/go/HEAD docker-compose (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy -o br-639c044e29b6 -j DROP ity_ECC.pem docker-entrypoin/usr/share/ca-certificates/mozilla/emSign_Root_CA_-_G1.crt /bin/test /.git/shallow_KPgit rtification_Auth-c ache/go/1.25.5/xprotocol.version=2 test -e (dns block)
• go.yaml.in
  • Triggering command: /update-job-proxy /update-job-proxy /internal/difc /home/REDACTED/go/HEAD docker-compose (dns block)
  • Triggering command: /update-job-proxy /update-job-proxy -o br-639c044e29b6 -j DROP ity_ECC.pem docker-entrypoin/usr/share/ca-certificates/mozilla/emSign_Root_CA_-_G1.crt /bin/test /.git/shallow_KPgit rtification_Auth-c ache/go/1.25.5/xprotocol.version=2 test -e (dns block)
• gopkg.in
  • Triggering command: /update-job-proxy /update-job-proxy -o br-639c044e29b6 -j DROP ity_ECC.pem docker-entrypoin/usr/share/ca-certificates/mozilla/emSign_Root_CA_-_G1.crt /bin/test /.git/shallow_KPgit rtification_Auth-c ache/go/1.25.5/xprotocol.version=2 test -e (dns block)
• this-host-does-not-exist-12345.com
  • Triggering command: /tmp/go-build3471895490/b282/mcp.test /tmp/go-build3471895490/b282/mcp.test -test.testlogfile=/tmp/go-build3471895490/b282/testlog.txt -test.paniconexit0 -test.timeout=10m0s -test.v=true se 5144330/b007/vetgithub.com/yosida95/uritemplate/v3 64/pkg/tool/linu-lang=go1.14 -p o_import.go -lang=go1.25 64/pkg/tool/linu-goversion -I /opt/hostedtoolc-c=4 695144330/b186//-nolocalimports /usr/bin/gcc --gdwarf-5 --64 5144330/b186/ ctor (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[refactor] Semantic Function Clustering Analysis - Code Organization Improvements</issue_title>
<issue_description>Analysis of 50 non-test Go files in the MCP Gateway repository identified 351 total symbols (184 functions, 167 methods) across 27 significant semantic clusters.

Key Findings

• 62 exact function name matches across different files
• 30 similar function names indicating potential consolidation opportunities
• 2 outlier functions in validation files
• 1 high-priority duplicate function for removal

Most significant findings:

1. Duplicate authentication header extraction (ExtractAgentIDFromAuthHeader wrapper)
2. Confusing SetVersion() naming (should be SetGatewayVersion())
3. Acceptable duplicates (Go idioms like Error(), Clone(), Get())

Priority 1: High Impact, Low Effort ⚡

1.1 Remove Duplicate Authentication Header Extraction

Issue: guard/context.go:68 has ExtractAgentIDFromAuthHeader() that simply wraps auth.ExtractAgentID().

Current code:

// internal/guard/context.go
func ExtractAgentIDFromAuthHeader(authHeader string) string {
    return auth.ExtractAgentID(authHeader)
}

Recommendation:

• ❌ Remove: guard.ExtractAgentIDFromAuthHeader()
• ✅ Use directly: auth.ExtractAgentID() at all call sites
• Benefit: Eliminates unnecessary wrapper, single source of truth
• Estimated effort: 1 hour

---

Priority 2: Medium Impact, Medium Effort 🔧

2.1 Clarify Version Management Function Names

Issue: Two SetVersion() functions with different purposes.

Current:

// internal/cmd/root.go
func SetVersion(v string) {
    version = v
    rootCmd.Version = v
    config.SetVersion(v)  // Calls the config version
}

// internal/config/validation_schema.go
func SetVersion(version string) {
    if version != "" {
        gatewayVersion = version
    }
}

Recommendation:

• Rename config.SetVersion() → config.SetGatewayVersion()
• Update call site in cmd/root.go
• Benefit: Clearer intent, reduces confusion
• Estimated effort: 30 minutes

2.2 Add Error Type Documentation

Issue: Multiple Error() implementations (idiomatic Go) but could use better documentation.

Affected types:

• ValidationError (config/rules)
• EnvValidationResult (config/validation_env)
• ViolationError (difc/labels)

Recommendation:

• Add godoc comments explaining each error type's purpose
• Benefit: Better developer experience when handling errors
• Estimated effort: 30 minutes

---

What's Working Well ✅

The analysis identified several well-organized areas:

• ✅ Sanitization Package (internal/logger/sanitize/) - Single-purpose, well-documented
• ✅ Logger Package - Clear separation of concerns (file, JSONL, markdown loggers)
• ✅ DIFC Package - Clean separation with strong type safety
• ✅ MCP Package - Focused protocol types with clear boundaries

---

Acceptable "Duplicates" (No Action Needed)

These patterns are idiomatic Go and should NOT be changed:

Multiple Error() Methods

• Why: Standard Go error interface implementation
• Types: ValidationError, EnvValidationResult, ViolationError
• ✅ Verdict: Keep as-is (proper Go design)

Multiple init() Functions

• Files: cmd/root.go, middleware/jqschema.go
• Why: Standard Go package initialization
• ✅ Verdict: No action needed

Multiple Clone() Methods

• Types: AgentLabels, Label
• Why: Type-specific deep copy for DIFC security
• ✅ Verdict: Good design, keep as-is

Multiple Get() Methods

• Types: AgentRegistry, Registry, SessionConnectionPool
• Why: Registry pattern with different key/value types
• ✅ Verdict: Keep as-is (generics would add complexity)

---

Implementation Checklist

Immediate Actions (Priority 1)

• Review ExtractAgentIDFromAuthHeader usage in guard/context.go
• Update call sites to use auth.ExtractAgentID() directly
• Remove wrapper function
• Run tests to verify no functionality broken

Short-term Actions (Priority 2)

• Rename config.SetVersion() to config.SetGatewayVersion()
• Update call site in cmd/root.go
• Add godoc comments to error types

---

Analysis Details

Files Analyzed (50 total)

By Package

• cmd (2 files): CLI initialization
• config (6 files): Configuration loading and validation
• difc (5 files): Security labels and enforcement
• guard (4 files): Security guard registry
• launcher (2 files): Backend process management
• logger (9 files): Logging infrastructure
• mcp (2 files): Protocol types and connections
• server (10 files): HTTP server and routing
• middleware (1 file): Request middleware
• auth (1 file...

• Fixes [refactor] Semantic Function Clustering Analysis - Code Organization Improvements #412

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