Junction Guard

Junction Guard

Purpose

Enforce the NK universe junction read-only rule: when Maxim detects that a target file path resolves through a filesystem junction or symlink (typically .mxm-system\ or .claude\ inside a sister project), it must refuse all write, delete, and git commit operations through that path. Reading is allowed.

Without this guard, an agent could accidentally write to the maxim source repo while operating in another project (e.g., mxm-simplification) — corrupting cross-project state and violating the data flow rule.

When This Skill Activates

• Any tool call that writes/edits/deletes a file
• Any git commit operation
• Any directory creation under a path that resolves through a junction

The Rule (from PROJECT_STRUCTURE_NK.md)

.mxm-system\ and .claude\ inside mxm-simplification\ are junctions. ✅ Reading through junctions is ALLOWED ❌ Writing through junctions is FORBIDDEN ❌ Deleting through junctions is FORBIDDEN ❌ Git commits through junctions are FORBIDDEN

This applies to ANY junction created by bootstrap/link-local-project.ps1 or any user-created junction pointing back at the maxim repo.

Detection Logic

For any write target path P:

1. Walk P upward to find any junction or symlink ancestor.
2. If an ancestor resolves to a path OUTSIDE the current project root, that ancestor is a JUNCTION (or cross-project symlink).
3. If the junction target is the Maxim source repo (E:\Projects\Maxim\maxim\ or symlink-equivalent): apply READ-ONLY rule.
4. If the junction target is any other project: apply CROSS-PROJECT WRITE rule (also forbidden).

Detection Commands

PowerShell:

$item = Get-Item -Path "<target-path>"
if ($item.LinkType -in @("Junction", "SymbolicLink")) {
    $resolved = $item.Target
    # Compare $resolved to current project root
}

Bash:

real_target=$(readlink -f "<target-path>")
project_root=$(pwd)
if [[ "$real_target" != "$project_root"* ]]; then
    echo "BLOCK: write resolves outside project root via junction"
fi

Enforcement

When a forbidden write is detected:

1. REFUSE the operation immediately. Do not proceed.
2. Output the error message:

   🔒 JUNCTION READ-ONLY VIOLATION
   
   Target path:  <target-path>
   Resolves to:  <real-resolved-path>
   Junction at:  <junction-ancestor>
   Reason:       <real-resolved-path> is outside the current project root
   
   This operation is FORBIDDEN by the NK universe junction rule.
   
   Allowed:
     ✅ Read this file through the junction
     ❌ Write / Edit / Delete / Commit through the junction
   
   To make this change:
     1. Open the source repo directly:
        cd <real-resolved-path-without-junction>
     2. Make the change there.
     3. Commit there.
     4. Pull updates here through the junction.
   

3. Log the attempt to .mxm-skills/junction-guard.log:

   {"timestamp":"2026-04-16T11:00:00Z","tool":"Write","target":"<path>","resolved":"<real>","blocked":true,"agent":"<calling-agent>"}
   

When NOT To Block

• The junction target IS the current project root (false positive — junction created in a way that loops back). Verify with absolute path comparison.
• The target is a regular file inside the project (not through any junction).
• The user has explicitly invoked /mxm-junction-bypass (NOT IMPLEMENTED — would require CSO approval).

Skill Output Format

Junction Guard Verdict: ALLOW | BLOCK
Target: [path]
Resolves to: [real-path or "same project"]
Crosses junction: YES | NO
Action: [proceed | refuse]
Logged to: .mxm-skills/junction-guard.log

Handoff

• BLOCK → return refusal to caller agent; log incident; suggest direct repo access
• ALLOW → return immediately, no action
• Repeated BLOCKs from same agent → escalate to CSO security-analyst (potential agent misconfiguration)

Frameworks Used

None. This is a structural safety enforcer, not a behavioral skill.

Source References

• PROJECT_STRUCTURE_NK.md (Junction Rule section)
• CLAUDE.d/session-memory.md (Junction Read-Only Enforcement section)
• bootstrap/link-local-project.ps1 (creates the junctions this guard protects)

Copyright (c) 2026 iSystematic Inc. Maxim product. BSL 1.1.