fix(differ): report a list envelope field added, removed or retyped

docs/architecture/ir-types.md

@@ -823,7 +823,7 @@ Wherever two inline models are folded into one by structural agreement — list-
 
 **Source per node.** Each node reads `deprecated` from one place: `Operation` from the Operation Object's own keyword; `Parameter` from any of the Parameter Object (after a `components.parameters` `$ref` is resolved), its inline `schema` and the component schema its `schema.$ref` points at — deprecated when any of the three says `deprecated: true`, so a `false` on one level does not stop a `true` on another; `ResponseHeader` from the Header Object only (after a `components/headers` `$ref` is resolved), never from its schema; `Field` from the property schema itself, a keyword written beside a `$ref` included, while the referenced model keeps its own and an `allOf` member's is not read — or, for a bare `$ref` to an array component, which has no model to keep the flag, from the component as well (see Array components); `Model` and `Enum` from the schema's own top-level keyword as described above. At every site the parser tests `=== true`: a `false`, absent or non-boolean keyword (`"yes"`, `1`) leaves the key absent, so the IR never carries anything but a literal `true`, on any of the six nodes. `EnumValue.deprecated` reads the value's own `const` member — an enum declared as a `oneOf`/`anyOf` of `const` schemas — by the same `=== true` rule, and is absent on every value of a plain `enum:` list, which has no per-value keyword (see Enum below).
 
-The differ compares the flag on every node that carries it — operation, parameter, response header, model, field, enum, enum value, webhook and webhook parameter — and reads it the way the parser writes it: only `true` is deprecated, so `false` and an absent key are the same thing, and a document that spells out `deprecated: false` diffs as unchanged against one that omits it. A flip is reported on the owning `-modified` change: `deprecatedChanged: true` on `operation-modified`, `model-modified`, `enum-modified` and `webhook-modified`, with `oldDeprecated`/`newDeprecated` beside it (present exactly when the flag is); a `param-deprecated-changed`, `header-deprecated-changed`, `field-deprecated-changed` or `value-deprecated-changed` entry, carrying the same two values and a `details` that reads `live → deprecated` or `deprecated → live`, in the change's `paramChanges`, `responseHeaderChanges`, `fieldChanges` or `valueChanges` for an operation's or a webhook's parameter, an operation's response header, a field or an enum value. A model, enum, operation or webhook whose only change is the flag is still reported, with an empty nested list. Becoming or ceasing to be deprecated changes no contract — the node is still there with the same shape — so every one of these is additive, in either direction; it still counts as `modified` in the summary, and a breaking change on the same node (a removed field beside the model's flag, a changed response beside the operation's, a retyped payload beside the webhook's) keeps the change breaking. Each flip is also mirrored into `behaviorChanges` as a `deprecated-changed` entry naming the node (`operation`, `parameter`, `response-header`, `model`, `field`, `enum`, `enum-value`, `webhook` or `webhook-parameter`) and copying `oldDeprecated`/`newDeprecated` from the change, the way a parameter default change is, so a changelog can say which way it went without reading both specs. Parameters are compared in every location a node carries them — an operation's path, query, header and cookie parameters, a webhook's header, query and cookie parameters — and matched by location and name, since a path `id` and a query `id` may sit on one operation and a webhook's header and query parameters may share a name — a header's name compared case-insensitively, so a header deprecated and respelled `x-pet-token` in one step is still the `X-Pet-Token` it was, and its flip is reported; every `paramChanges` entry carries `paramLocation` to say which one it is about. A response header's flag is compared on every response entry that declares headers — the primary and every other 2xx/3xx entry, every error, the `default` and every range — with headers matched by name case-insensitively, and every `responseHeaderChanges` entry carries its `statusCode` or `fallback` to say which entry it is about (see Response Headers above).
+The differ compares the flag on every node that carries it — operation, parameter, response header, model, field, list envelope field, enum, enum value, webhook and webhook parameter — and reads it the way the parser writes it: only `true` is deprecated, so `false` and an absent key are the same thing, and a document that spells out `deprecated: false` diffs as unchanged against one that omits it. A flip is reported on the owning `-modified` change: `deprecatedChanged: true` on `operation-modified`, `model-modified`, `enum-modified` and `webhook-modified`, with `oldDeprecated`/`newDeprecated` beside it (present exactly when the flag is); a `param-deprecated-changed`, `header-deprecated-changed`, `field-deprecated-changed` or `value-deprecated-changed` entry, carrying the same two values and a `details` that reads `live → deprecated` or `deprecated → live`, in the change's `paramChanges`, `responseHeaderChanges`, `fieldChanges`, `envelopeFieldChanges` or `valueChanges` for an operation's or a webhook's parameter, an operation's response header, a field, an operation's list envelope field (`pagination.envelopeFields`, matched by name while both specs paginate) or an enum value. A model, enum, operation or webhook whose only change is the flag is still reported, with an empty nested list. Becoming or ceasing to be deprecated changes no contract — the node is still there with the same shape — so every one of these is additive, in either direction; it still counts as `modified` in the summary, and a breaking change on the same node (a removed field beside the model's flag, a changed response beside the operation's, a retyped payload beside the webhook's) keeps the change breaking. Each flip is also mirrored into `behaviorChanges` as a `deprecated-changed` entry naming the node (`operation`, `parameter`, `response-header`, `model`, `field`, `envelope-field`, `enum`, `enum-value`, `webhook` or `webhook-parameter`) and copying `oldDeprecated`/`newDeprecated` from the change, the way a parameter default change is, so a changelog can say which way it went without reading both specs. Parameters are compared in every location a node carries them — an operation's path, query, header and cookie parameters, a webhook's header, query and cookie parameters — and matched by location and name, since a path `id` and a query `id` may sit on one operation and a webhook's header and query parameters may share a name — a header's name compared case-insensitively, so a header deprecated and respelled `x-pet-token` in one step is still the `X-Pet-Token` it was, and its flip is reported; every `paramChanges` entry carries `paramLocation` to say which one it is about. A response header's flag is compared on every response entry that declares headers — the primary and every other 2xx/3xx entry, every error, the `default` and every range — with headers matched by name case-insensitively, and every `responseHeaderChanges` entry carries its `statusCode` or `fallback` to say which entry it is about (see Response Headers above).
 
 ## Enum