FPF Reasoning

# 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.

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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

| Situation | Action | What it does | |-----------|--------|--------------| | Evidence is old but decision is still good | Refresh | Re-run the test, get fresh evidence | | Decision is obsolete, needs rethinking | Deprecate | Downgrade hypothesis, restart evaluation | | Accept risk temporarily | Waive | Record the risk acceptance with deadline |

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Action (Run-Time)

Step 1: Generate Freshness Report

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

Step 2: Present Report

```markdown ## Evidence Freshness Report

EXPIRED (Requires Action)

| Evidence | Hypothesis | Expired | Days Overdue | |----------|------------|---------|--------------| | ev-benchmark-2024-06-15 | redis-caching | 2024-12-15 | 45 | | ev-security-2024-07-01 | auth-module | 2025-01-01 | 14 |

STALE (Warning)

| Evidence | Hypothesis | Expires | Days Left | |----------|------------|---------|-----------| | ev-loadtest-2024-10-01 | api-gateway | 2025-01-20 | 5 |

FRESH

| Evidence | Hypothesis | Expires | |----------|------------|---------| | ev-unittest-2025-01-10 | validation-lib | 2025-07-10 |

WAIVED

| Evidence | Waived Until | Rationale | |----------|--------------|-----------| | ev-perf-old | 2025-02-01 | Migration pending | ```

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:

```markdown # In .fpf/evidence/deprecate-auth-module-2025-01-15.md --- id: deprecate-auth-module-2025-01-15 hypothesis_id: auth-module action: deprecate from_layer: L2 to_layer: L1 created: 2025-01-15T10:00:00Z ---

# Deprecation: auth-module

Reason: Evidence expired, technology landscape changed

Next Steps: Run `/fpf:propose-hypotheses` to explore alternatives ```

1. Move the hypothesis file:
2. ```bash
3. mv .fpf/knowledge/L2/auth-module.md .fpf/knowledge/L1/auth-module.md
4. ```

#### Waive

User: "Waive the benchmark until February"

1. Create waiver record:

```markdown # In .fpf/evidence/waiver-benchmark-2025-01-15.md --- id: waiver-benchmark-2025-01-15 evidence_id: ev-benchmark-2024-06-15 waived_until: 2025-02-01 created: 2025-01-15T10:00:00Z ---

# Waiver: ev-benchmark-2024-06-15

Evidence: ev-benchmark-2024-06-15 Hypothesis: redis-caching Waived Until: 2025-02-01 Rationale: Migration pending, will re-run after completion

Accepted By: User Created: 2025-01-15

WARNING: This evidence returns to EXPIRED status after 2025-02-01. ```

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Natural Language Usage

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

Example Workflow

``` User: /fpf:decay

Agent shows report with stale evidence

User: Waive the benchmark until February, we'll re-run it after the migration.

Agent: Creating waiver for ev-benchmark-2024-06-15 until 2025-02-01. Rationale: "Re-run after migration"

[Creates .fpf/evidence/waiver-benchmark-2025-01-15.md]

User: The vendor API is being discontinued. Deprecate that decision.

Agent: Deprecating hypothesis-vendor-api from L2 to L1. [Moves file, creates deprecation record]

Next step: Run /fpf:propose-hypotheses to explore alternatives. ```

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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.

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Audit Trail

All actions are logged:

| Action | What's Recorded | |--------|-----------------| | Deprecate | from_layer, to_layer, reason, date | | Waive | evidence_id, until_date, rationale, date |

• Files created in `.fpf/evidence/`:
• `deprecate-{hypothesis}-{date}.md`
• `waiver-{evidence}-{date}.md`

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Common Workflows

Weekly Maintenance ``` /fpf:decay # See what's stale # For each stale item: refresh, deprecate, or waive ```

Pre-Release ``` /fpf:decay # Check for stale decisions # Either refresh evidence or explicitly waive with documented rationale # Waiver rationales become part of release documentation ```

After Major Change ``` # Dependency update, API change, security advisory... /fpf:decay # See what's affected # Deprecate obsolete decisions # Start new hypothesis cycle for replacements ```