docs(lost-substrate): full Day-1/2/3 corruption-triage substrate continuation (off-trunk; PR #756 squashed Day-0 only)

docs/lost-substrate/artifacts/2026-04-29-corruption/gc-config-snapshot.txt

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+# git gc config snapshot — 2026-04-29 corruption triage
+# (read-only inspection; no mutation)
+
+gc.auto = (unset; default ~6700)
+gc.autoPackLimit = (unset; default 50)
+gc.pruneExpire = (unset; default 2.weeks.ago)
+gc.reflogExpire = (unset; default 90.days.ago)
+gc.reflogExpireUnreachable = (unset; default 30.days.ago)
+gc.worktreePruneExpire = (unset; default 3.months.ago)

docs/lost-substrate/artifacts/2026-04-29-corruption/hour-05Z-show-ref.txt

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+d9feb3f08603e37118491e26527c03e6e5760d5b refs/heads/chore/heartbeat-batch-2026-04-26-hour-05Z
+d9feb3f08603e37118491e26527c03e6e5760d5b refs/remotes/origin/chore/heartbeat-batch-2026-04-26-hour-05Z

docs/lost-substrate/artifacts/2026-04-29-corruption/triage-report.md

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+# Corruption triage — 2026-04-29 — empirical artifact
+
+This file captures the exact commands run, the raw outputs (in
+sibling files), and the conclusion drawn. It exists so a future
+reader can verify the prose conclusions in the ledger against the
+artifacts, rather than trusting the summary.
+
+## Sibling artifact files
+
+| File | Source command |
+|---|---|
+| `fsck-full.txt` | `git fsck --full --no-progress` (reflog-inclusive) |
+| `fsck-full-no-reflogs.txt` | `git fsck --full --no-reflogs --no-progress` |
+| `fsck-connectivity.txt` | `git fsck --connectivity-only --no-progress` |
+| `rev-list-all-objects.txt` | `git rev-list --objects --all` |
+| `rev-list-all-objects.err` | stderr from the above (corruption errors) |
+| `gc-config-snapshot.txt` | per-key `git config --get gc.*` snapshot |
+
+All files are point-in-time evidence; do not edit.
+
+## Two corrupt objects under triage
+
+| SHA | Type | Size | Source path |
+|---|---|---|---|
+| `9bf2daee3ce53c88633824f9532a0158aaa92ed9` | blob (recovered from origin) | 16,455,417 bytes | unknown — large blob |
+| `8d5e67fd313573855848705e4af114f3ff0eecbc` | blob (corrupt loose, locally) | unrecoverable from origin | `docs/hygiene-history/loop-tick-history.md` (intermediate version) |
+
+## Three-bucket reachability — `8d5e67fd`
+
+Per Amara 2026-04-29: `git fsck` reachability is mode-dependent
+(reflog-inclusive vs `--no-reflogs`). A correct classification
+distinguishes three buckets:
+
+| Bucket | Definition | Verdict for `8d5e67fd` |
+|---|---|---|
+| A | Live branch / tag / ref reachable | **YES** — `refs/heads/chore/heartbeat-batch-2026-04-26-hour-05Z` reaches it (local-only; the same-named remote-tracking ref is stale — origin no longer has the branch) |
+| B | Reflog / stash / local-recovery reachable | Indeterminate from this scan; reflog scan was reflog-inclusive fsck (showed dangling adjacency); `refs/stash` is empty |
+| C | Dangling / unreachable only | **NO** — bucket A applies, so C does not |
+
+### Verifying bucket A
+
+```text
+$ git rev-list --objects --all | grep 8d5e67fd
+8d5e67fd313573855848705e4af114f3ff0eecbc docs/hygiene-history/loop-tick-history.md
+
+$ git for-each-ref ... | per-ref rev-list grep
+ref=refs/heads/chore/heartbeat-batch-2026-04-26-hour-05Z   → reaches it
+ref=refs/remotes/origin/chore/heartbeat-batch-2026-04-26-hour-05Z → reaches it (stale)
+```
+
+### Verifying the remote-tracking ref is stale
+
+```text
+$ git ls-remote origin refs/heads/chore/heartbeat-batch-2026-04-26-hour-05Z
+(empty — origin no longer has this branch)
+
+$ fresh-clone --branch chore/heartbeat-batch-2026-04-26-hour-05Z
+fatal: Remote branch chore/heartbeat-batch-2026-04-26-hour-05Z not found in upstream origin
+```
+
+### Content-equivalence verification — `8d5e67fd`
+
+Per Amara's correction: verify squash-preservation by **content**,
+not by ancestry vibe.
+
+```text
+$ BR=refs/heads/chore/heartbeat-batch-2026-04-26-hour-05Z
+$ OBJ=8d5e67fd313573855848705e4af114f3ff0eecbc
+
+$ git ls-tree -r "$BR" | grep "$OBJ"
+(no path-match — corrupt blob is NOT at the branch tip)
+
+$ git show "$BR":docs/hygiene-history/loop-tick-history.md | head -1
+# Loop-tick history          ← branch tip's tick-history.md is readable
+
+$ git diff --name-status origin/main..."$BR" \
+    -- docs/hygiene-history/loop-tick-history.md
+M docs/hygiene-history/loop-tick-history.md   ← diff succeeds
+
+$ git log --oneline -1 "$BR"
+d9feb3f chore(loop-tick-history): hour-05Z bundle close 2026-04-26T05:59:36Z ...
+```
+
+**Branch tip is clean.** The corrupt blob `8d5e67fd` is from
+the branch's **intermediate history** (an earlier commit on the
+same branch path), NOT the current tip. The branch is also NOT
+an ancestor of `main` (its tip is post-squash-merge and
+abandoned), and `main` carries the equivalent content under a
+different blob (`de670f72d6fd34208d04863818288d764150a151`).
+
+```text
+main's tick-history blob: de670f72d6fd34208d04863818288d764150a151
+branch-tip's blob:        (different, clean — readable via git show)
+corrupt blob:             8d5e67fd313573855848705e4af114f3ff0eecbc
+                          ← appears only in intermediate history
+```
+
+## Final classification — `8d5e67fd`
+
+```text
+CORRUPT_BLOB_REFERENCED_BY_LIVE_LOCAL_BRANCH_AND_STALE_REMOTE_TRACKING_REF
+```
+
+(sub-bucket of bucket A under the three-bucket schema; refined
+sub-condition: branch TIP is clean, corrupt blob is in
+intermediate history of the branch only.)
+
+Substrate-loss assessment:
+- **Current-state use** (checkout / hard-reset-to-tip / diff vs
+  main): zero impact. Branch tip and main are both readable.
+- **Bisect-through-pre-merge-history**: impacted. Bisecting
+  `loop-tick-history.md` through this branch's intermediate
+  revisions would surface the corrupt blob; that pre-merge
+  bisect-step granularity is the only thing actually lost,
+  and it's a niche use case for a stale post-merge local
+  branch.
+
+## Hard-reset readiness — qualified statement
+
+```text
+This corruption does not appear to affect current main, but it
+DOES affect at least one live local branch (specifically, the
+intermediate history of refs/heads/chore/heartbeat-batch-2026-
+04-26-hour-05Z). Hard reset / branch cleanup remains blocked
+until the branch's content is classified as preserved,
+obsolete, or explicitly abandoned.
+```
+
+Branch-tip checkout / hard-reset-to-tip is fine. Reading
+intermediate-history blobs would surface the corruption.
+
+## Stale remote-tracking ref — evidence, not origin recovery
+
+```text
+$ git show-ref | grep 'chore/heartbeat-batch-2026-04-26-hour-05Z'
+d9feb3f08603e37118491e26527c03e6e5760d5b refs/heads/chore/heartbeat-batch-2026-04-26-hour-05Z
+d9feb3f08603e37118491e26527c03e6e5760d5b refs/remotes/origin/chore/heartbeat-batch-2026-04-26-hour-05Z
+                                         ↑ same SHA → ref is stale, not authoritative
+
+$ git ls-remote --heads origin chore/heartbeat-batch-2026-04-26-hour-05Z
+(empty — origin no longer has this branch)
+```
+
+The remote-tracking ref is **stale** — origin deleted the
+branch (presumably after squash-merge), but the local repo
+still carries the same-named ref under
+`refs/remotes/origin/...`. This stale ref is evidence about
+the prior state of origin; it is NOT proof origin currently
+has the object. Do not prune it during triage — `git fetch
+--prune origin` and `git remote prune` would remove it, and
+that's a destructive cleanup decision under the same rule as
+GC.
+
+```text
+Stale remote-tracking ref is evidence, not origin recovery.
+Do not prune it while investigating lost substrate.
+```
+
+## Cleanup posture
+
+```text
+Cleanup is a destructive decision, not a repair step.
+```
+
+`git gc` / `git prune` / `git repack -Ad` / `git fsck --lost-found`
+remain forbidden during triage. Auto-gc thresholds are at default
+(per `gc-config-snapshot.txt`); below-threshold loose-object count
+means auto-gc is not imminent, but the discipline is "no implicit
+cleanup decision" not "we have time."
+
+A future cleanup may remove this unreachable/corrupt evidence, so
+cleanup must wait until related dangling/reflog/stash surfaces
+are classified and either preserved or explicitly abandoned.
+
+## Composes with
+
+- `docs/lost-substrate/inventory-ledger-2026-04-29.md` — the
+  inventory ledger that surfaced these findings.
+- `memory/feedback_corruption_triage_discipline_object_health_incident_aaron_amara_2026_04_29.md`
+  — the durable discipline rule.
+
+## Distilled keepers (Amara 2026-04-29)
+
+```text
+A corrupt object is not a backlog item — it is a substrate health incident.
+Do not prune the evidence while investigating lost evidence.
+Recoverable-from-origin requires fresh-clone cat-file type + size verification.
+Cleanup is a destructive decision, not a repair step.
+Corruption lane means exclusive lane.
+If corruption is the incident, everything else is noise.
+```