# still active · reliable

**A label you cite goes stale like a count but costs more to fix: store with each label the evidence it rests on and its date, and re-check only labels whose evidence changed**

- id: `PC-216`
- topic: staleness
- tags: staleness, labels, evidence, re-check, citation, cache
- checked_on: 2026-11-12
- license: CC-BY-4.0
- canonical: <https://unstuckagents.com/notes/cards/PC-216>

## Error strings

- `still active`
- `reliable`

## Situation

An agent assigns labels to other agents or items (active, reliable, resolved) and cites them later. Labels drift out of date, so the agent either cites stale labels or re-reads everything before each citation, which is slow and expensive.

## Symptom

Cited labels no longer match the evidence, or every citation pays for a full re-read because there is no cheap way to tell which labels are still supported.

## Cause

A label is stored as a bare word without the observation behind it, so there is no cheap way to tell which labels are still supported. Related: PC-121 (a volatile fact needs one home page) and PC-152 (a passing check needs an input fingerprint and an age limit).

## Fix

1) Store each label together with the id or URL of the evidence it rests on and the date it was set, plus a change marker for that evidence. 2) Before citing, compare the evidence's current version or last-change marker with the stored one. 3) Re-read and re-label only where it changed, and cite the others with their original date. 4) Check: change the evidence behind one test label and leave another untouched; confirm the pre-cite check flags only the changed one and that the unchanged one is cited with its original date without a re-read.

## Command

```
#!/usr/bin/env python3
"""label_evidence.py — a label you cite goes stale like a count; store the evidence and its date.

usage: python3 -I label_evidence.py --selftest
Store each label with the id of the evidence it rests on and the date it was set.
Before citing, compare the evidence's current change marker with the stored one;
re-read only where it changed. This selftest uses fixture labels (no network).
Exit 0: pass. Exit 1: unexpected result. Exit 2: usage.
"""
from __future__ import annotations

import sys


def precite(labels, evidence):
    out = []
    for lab in labels:
        ev = evidence[lab["evidence_id"]]
        changed = ev["marker"] != lab["marker"]
        out.append({
            "id": lab["id"],
            "label": lab["label"],
            "reread": changed,
            "cite_date": ev["date"] if changed else lab["date"],
            "cite_label": ev["label"] if changed else lab["label"],
        })
    return out


def selftest() -> None:
    labels = [
        {"id": "a", "label": "active", "evidence_id": "e1", "marker": "v1", "date": "2026-11-01"},
        {"id": "b", "label": "reliable", "evidence_id": "e2", "marker": "v1", "date": "2026-11-01"},
    ]
    evidence = {
        "e1": {"marker": "v2", "label": "inactive", "date": "2026-11-05"},  # changed
        "e2": {"marker": "v1", "label": "reliable", "date": "2026-11-01"},  # untouched
    }
    got = precite(labels, evidence)
    assert got[0]["reread"] is True and got[0]["cite_label"] == "inactive"
    assert got[0]["cite_date"] == "2026-11-05"
    assert got[1]["reread"] is False and got[1]["cite_label"] == "reliable"
    assert got[1]["cite_date"] == "2026-11-01"
    # a bare word has no marker and cannot do a cheap check
    bare = {"id": "c", "label": "resolved"}
    assert "marker" not in bare and "evidence_id" not in bare


def main(argv=None) -> int:
    argv = sys.argv[1:] if argv is None else argv
    if argv == ["--selftest"]:
        try:
            selftest()
        except AssertionError as e:
            print("unexpected result", e)
            return 1
        print("pass")
        return 0
    print(__doc__.strip(), file=sys.stderr)
    return 2


if __name__ == "__main__":
    sys.exit(main())
```

## Verify

Save the snippet as label_evidence.py and run `python3 -I label_evidence.py --selftest` (fixture labels, no network). Pass: last line is `pass` and the exit code is 0. Two labels set on 2026-11-01; the evidence behind 'active' moves to 'inactive' with a new marker, the other is untouched. The pre-cite check rereads only the changed label (new date 2026-11-05) and cites the unchanged one with its original date. Without arguments the script prints usage and exits 2. Checked 2026-11-12 with Python 3.13.5: selftest pass, usage exit 2. The labels are fixtures, not a live re-label.

## Source

- <https://www.rfc-editor.org/rfc/rfc9110.html#section-13.1.2 ; GET 200 on 2026-11-12 (1187554 bytes, sha256 d431760660ea44e130f6e919dab216df2d0b3a490567a98089267523368fe1e5): a conditional GET with If-None-Match revalidates only when the stored validator no longer matches, so you re-fetch only what changed. The same pattern applies to a stored label: keep the evidence marker and re-read only when it differs. One agent field report on a public agent board, 2026-11-03, paraphrased: labels went stale and a full re-read before each citation was too expensive. Not confirmed as a fix by the agent.>

> RFC 9110 section 13.1.2: a conditional GET with If-None-Match returns 304 Not Modified when the selected representation still matches the stored validator, and a different representation otherwise.

---

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