Say which operator actions are debt and which are just operations

An intervention is an action required to recover, repair, unblock or correct
behaviour that should have proceeded on its own. A deploy restart, a planned
upgrade and burn-in setup are none of those, and recording them would inflate
operator cost with work Orchestra is expected to need.

Policy rather than schema. worker_restart is the one kind that spans both
sides, and it stays one kind until someone actually misuses it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CVbaKucEYBjMqVeUgJUsc1

DEBT-DESIGN.md

@@ -408,3 +408,74 @@ which is the priority function slice one deliberately omitted.
 
 None of these required a schema commitment to discover. That was the point of
 making the first slice read-only.
+
+## The invariant slice B was written against
+
+**A projection must never manufacture provenance to make evidence easier to
+classify.** `task=None` is better than a confident lie.
+
+Both defects the first live run of durable observations exposed were failures
+of exactly this rule, and both looked perfectly reasonable in code:
+
+- **False attribution.** The worker's ring outlives the work it describes, so
+  binding its entries to whatever task the worker is running now produced a
+  clean, well-formed, wrong association between an old failure and an unrelated
+  task. The task is read from the observation itself, and only an observation
+  that names no task belongs to the current lease.
+- **Manufactured recurrence.** Treating "still present in the ring" as "it
+  happened again" turned one failure into four incidents. Presence is not
+  occurrence: an incident opens only when the entry advances past what has
+  already been accounted for, and that high-water mark survives the close.
+
+Either one would have corrupted the ledger while every number in it stayed
+plausible, which is the specific way this repo's bugs have always presented.
+
+## Signatures are frozen at write time
+
+The signature is computed when an incident is recorded and stored in the event.
+Re-projecting an old log with a newer normalizer therefore changes nothing:
+running one history through the build before and after the pane-name fix
+produced identical output.
+
+That is the intended behavior. An event must not silently change meaning
+because normalization code changed. Repairing historical signatures is an
+explicit migration or reclassification event, never a different projection
+result from the same log.
+
+## What counts as a manual intervention
+
+An intervention is an operator action required to recover, repair, unblock or
+correct behaviour that should otherwise have proceeded autonomously. The
+ledger measures what the system costs to keep running, so routine operation
+does not belong in it.
+
+Counts:
+
+```text
+transaction_cleanup
+forced_release
+state_repair
+manual_requeue          when recovery failed and a human had to requeue
+manual_phase_recovery
+worker_restart          only when restarting is itself the repair
+```
+
+Does not count:
+
+```text
+deploy restart
+planned upgrade
+configuration rollout
+normal shutdown and start
+deliberate burn-in setup
+```
+
+The distinction is policy rather than schema. `worker_restart` is the one kind
+that spans both sides, and it stays a single kind until someone actually
+misuses it; a field added before the confusion exists is a guess about how it
+will be misread.
+
+The first live consequence: the deploy restart of `79d2053` was not recorded,
+and `manual_intervention` stayed in the gap list afterwards. That is the
+correct result. Orchestra can record the evidence and this history contains
+none, which is an honest gap rather than synthetic evidence.