Dead-letter diagnostics lose history on re-index (firstSeenAt reset to the rebuild)

[norgejbb-byte]

Expected

A dead-letter's firstSeenAt reflects when the failure was first observed and
survives an index rebuild, so operators can distinguish long-standing failures
from new ones and see the trend.

Observed (bytes)

Public surface: GET https://community-production-9ab1.up.railway.app/api/dacs/status
(OpenAPI: params deadLetterLimit ≤ 100, locator ^stor-[0-9a-f]{40}$; response
indexer.deadLetterDiagnostics {scope:"storage-read", total, byCode, byKind, query, returned, hasMore, items[]}).

At ?deadLetterLimit=100: total: 56, byCode: {"STORAGE_UNREADABLE": 56}, and
all 56 items[].firstSeenAt fall within a single ~4.7-hour window
(2026-07-26T13:44:32.219Z – 2026-07-26T18:25:05.033Z) — i.e. clustered at the
index rebuild, not spread across the period the failures actually span. Each item
also shows retryState: "exhausted".

The failure population is not new: Community #20 (2026-07-13 era) reports prior
dead-letter counts of 38 and 41; the count has since climbed to 56.
Those earlier entries predate the rebuild, yet every firstSeenAt now reads as
the rebuild time — the original first-observed history was lost on re-index.

Repro

curl -s 'https://community-production-9ab1.up.railway.app/api/dacs/status?deadLetterLimit=100' \
 | jq '.indexer.deadLetterDiagnostics
        | {total, byCode,
           firstSeenMin: ([.items[].firstSeenAt]|min),
           firstSeenMax: ([.items[].firstSeenAt]|max)}'
# → total 56; byCode {STORAGE_UNREADABLE:56}; min/max firstSeenAt inside one ~4.7h window
# compare against the counts (38, 41) in Community #20 to see the pre-rebuild history

Cross-links

• What is being dead-lettered (logical-as-physical bundle reads): Indexer dereferences §10.4.2 LOGICAL bundle addresses as physical storage locators → STORAGE_UNREADABLE dead letters #45.
• Prior counts / history: Community /api/dacs/status dead-letters ~11% of artifacts with no per-artifact reason surfaced #20.

[randomblocker]

Fixed in draft PR #49. Active dead-letter retry state remains chain-scoped, while first observation is now persisted in separate historical storage and survives rebuild/reset. Regression coverage verifies the original firstSeenAt is retained; CI is green.