decay

Evidence Freshness Management

Manages evidence freshness by identifying stale decisions and providing governance actions. Implements FPF B.3.4 (Evidence Decay).

Key principle: Evidence is perishable. Decisions built on expired evidence carry hidden risk.

Quick Concepts

What is "stale" evidence?

Every piece of evidence has a valid_until date. A benchmark from 6 months ago may no longer reflect current system performance. A security audit from before a major dependency update doesn't account for new vulnerabilities.

When evidence expires, the decision it supports becomes questionable - not necessarily wrong, just unverified.

What is "waiving"?

Waiving = "I know this evidence is stale, I accept the risk temporarily."

Use it when:

• You're about to launch and don't have time to re-run all tests
• The evidence is only slightly expired and probably still valid
• You have a scheduled date to refresh it properly

A waiver is NOT ignoring the problem - it's explicitly documenting that you know about the risk and accept it until a specific date.

The Three Actions

Action (Run-Time)

Step 1: Generate Freshness Report

1. List all evidence files in .fpf/evidence/
2. For each evidence file:
   • Read valid_until from frontmatter
   • Compare with current date
   • Classify as FRESH, STALE, or EXPIRED

Step 2: Present Report

## Evidence Freshness Report
 
### EXPIRED (Requires Action)
 
| Evidence | Hypothesis | Expired | Days Overdue |
|----------|------------|---------|--------------|
| ev-benchmark-2024-06-15 | redis-caching | 2024-12-15 | 45 |

Step 3: Handle User Actions

Based on user response, perform one of:

Refresh

User: "Refresh the redis caching evidence"

1. Navigate to the hypothesis in .fpf/knowledge/L2/
2. Re-run validation to create fresh evidence

Deprecate

User: "Deprecate the auth module decision"

1. Move hypothesis from L2 to L1 (or L1 to L0)
2. Create deprecation record:

3. Move the hypothesis file:

Waive

User: "Waive the benchmark until February"

1. Create waiver record:

Natural Language Usage

You don't need to memorize evidence IDs. Just describe what you want.

Example Workflow

WLNK Principle

A hypothesis is STALE if any of its evidence is expired (and not waived).

This is the Weakest Link (WLNK) principle: reliability = min(all evidence). One stale piece makes the whole decision questionable.

Audit Trail

All actions are logged:

Files created in .fpf/evidence/:

• deprecate-{hypothesis}-{date}.md
• waiver-{evidence}-{date}.md

Common Workflows

Weekly Maintenance

Pre-Release

After Major Change