spec(intent-4): cross-skill deregistration needs a non-mirroring transport

CHANGELOG.md

@@ -326,6 +326,16 @@ version 2: its `{{ … }}` sequences become substitution points, and its
 
 ### 2
 
+- §8.4 — the cross-skill deregistration (source ≠ target) is carried
+  only by a transport that delivers `ovos.skill.deregister` on its own;
+  a producer **MUST NOT** emit it through a client that mirrors the
+  topic onto `detach_skill`, whose predecessor handlers act on the
+  source. Self-deregistration is unaffected. A malformed emission
+  (payload without `skill_id`) has no target, so spec handlers remove
+  nothing. The mirrored predecessor acts on it as a
+  self-deregistration. The mirror
+  runs both ways, so emitting `detach_skill` directly does not avoid
+  it. Divergence row for `detach_skill` records both shapes.
 - §8.6 (new) — `ovos.skill.loaded`, the session-keyed load announcement
   with a registered `capabilities` vocabulary (`fallback`, `common_query`,
   `converse`); withdrawn by `ovos.skill.deregister`. §10.3 (new) —

appendix/divergences.md

@@ -518,7 +518,7 @@ a number of predecessor names. The mapping:
 | `padatious:register_intent` | `ovos.intent.register.template` | Same content, structured payload. |
 | `padatious:register_entity` | `ovos.entity.register` | Entities are not Padatious-specific. |
 | `detach_intent` | `ovos.intent.deregister` | Identity now expressed as the structured triple, not the munged `skill_id:intent_name` string. |
-| `detach_skill` | `ovos.skill.deregister` | |
+| `detach_skill` | `ovos.skill.deregister` | Predecessor handlers resolve the skill from `context`. A client that mirrors `ovos.skill.deregister` onto `detach_skill` therefore turns two shapes into a self-deregistration on the mirrored copy: a cross-skill deregistration (payload names another skill), which removes the source together with the target, and a malformed one (payload omits `skill_id`), which the spec handlers reject and the predecessor handlers act on. The cross-skill form of INTENT-4 §8.4 needs the mirror off (`emit_legacy=false` in ovos-bus-client); the malformed form is unsafe on a mirroring client rather than merely ignored. The mirror runs both ways through two flags: `emit_legacy` copies `ovos.skill.deregister` onto `detach_skill`, and `modernize` copies `detach_skill` onto `ovos.skill.deregister`. So a producer emitting `detach_skill` directly reaches the same consumers, and the source is removed whichever wire it uses. |
 | `mycroft.skill.enable_intent` / `mycroft.skill.disable_intent` | `ovos.intent.enable` / `ovos.intent.disable` | First-class topics under v1, with the prefix dropped. |
 | `mycroft.skills.loaded` | `ovos.skill.loaded` | Session-keyed, carries `capabilities` instead of a filesystem `path` and display `name`. `mycroft.skills.loading_failure` has no successor: a skill that did not load announces nothing. |
 | `skillmanager.list` / `mycroft.skills.list` | `ovos.skills.list` / `.list.response` | A `response` derivation with a `skills` array instead of a map keyed by skill id; entries carry `session_id`, `capabilities` and an intent count instead of `active`. |

intent-4.md

@@ -607,6 +607,32 @@ SHOULD emit `ovos.skill.deregister` carrying the satellite's session
 in `context` for every skill the satellite registered when the
 satellite disconnects (OVOS-BRIDGE-1 §3).
 
+The payload `skill_id` is the target and `context.skill_id` the
+source (§3.2), so a source may deregister a skill other than itself.
+That **cross-skill form** is carried only by a transport that
+delivers `ovos.skill.deregister` on its own. A client that mirrors
+the topic onto its predecessor `detach_skill` (appendix, divergences)
+hands the mirrored copy to every consumer whose predecessor handler
+resolves the skill from `context`, and the source's own
+registrations are removed together with the target's. A producer
+**MUST NOT** emit a cross-skill deregistration through a client that
+mirrors registration topics onto their predecessors. A skill
+deregistering itself is unaffected, because source and target
+coincide. The same transport property reaches a **malformed**
+emission: a Message whose payload omits `skill_id`, a required
+field of the §3.2 table, has no target, so a consumer of this
+section removes nothing, but its mirrored copy carries
+the emitter in `context`, and a predecessor handler acts on it as a
+self-deregistration. Through a mirroring client, then, a producer
+that omits the target loses its own registrations rather than
+nothing. The mirror runs in both directions: a client that mirrors
+the spec topic onto `detach_skill` also delivers a `detach_skill`
+emission under `ovos.skill.deregister`, so emitting the predecessor
+directly reaches the same consumers and the source is removed
+whichever wire the producer uses. The mirror is a setting of the
+migration tooling, not a property of any handler; the cross-skill
+form is available once the deployment's clients stop mirroring.
+
 Deregistering an intent, entity, or skill that is not currently
 registered is a **no-op**: registrations are fire-and-forget, every
 plugin processes the message independently, and any plugin without a