Output Trust Check

Output Trust Check

Prerequisites & Dependencies

• Python 3.10+ (for output parsing and truncation detection)
• Access to all tool output channels (bash, PowerShell, tool API responses)
• No external runtime dependencies

Execution Steps

1. Detect truncation: After any tool call that returns output, check for these truncation indicators:

   • Bash: output truncated message, $? non-zero due to SIGPIPE
   • PowerShell: Output wrapped in ..., WriteWarning about buffer size
   • API responses: truncated flag, has_more = false, partial content returned

2. Refuse decision on truncated data: If truncation is detected, immediately:

   • Mark the output segment as UNTRUSTED
   • Do not incorporate the truncated portion into any decision, invariant, or completion claim
   • Automatically request the tail window or a targeted follow-up

3. Request tail or targeted follow-up: After flagging truncation, one of:

   • Re-run the tool with increased limit or offset parameters
   • Apply a targeted grep/Select-String to the source data for the missing portion
   • Request a specific file range or line number range

4. Flag encoding anomalies: Inspect output for:

   • UTF-16 BOM (\xFF\xFE or \xFE\xFF) at start
   • NUL bytes (\x00) embedded in text strings
   • Mixed encoding markers (e.g., CP1252 vs UTF-8 sequences)
   • On detection, annotate output with encoding-suspect: true and re-parse as UTF-8 after stripping BOM/NUL

5. Output trust flag: Return a structured trust metadata object alongside any output:

   {
     "output": "<captured text>",
     "trusted": <boolean>,
     "truncated": <boolean>,
     "encoding_suspect": <boolean>,
     "note": "<human-readable explanation if untrusted>"
   }
   

Trust Workflow Example

Tool call: rg "pattern" . --max-count 5
Normal output: matches found
→ Trusted: true, Truncated: false

Tool call: head -n 10 large-file.log
Output: first 10 lines, then "output truncated (use -n 50)"
→ Trusted: false, Truncated: true
→ Agent requests: "Please provide the next 10 lines starting at line 11"

Windows PowerShell Notes

• Truncation detection: check $MaximumOutput and Write-Warning about buffer limits
• Encoding inspection: use [System.Text.Encoding]::UTF8.GetBytes() to detect BOM/NUL corruption
• Auto-request pattern: Get-Content -Path file.txt -Skip N -Tail 10 for tail windows