R8: page actions as words, one spelling per keyword, lowercase keywords (#752)

[ako]

Closes #752 (R8, phase 3.2 of the beta syntax freeze; tracking #714).

What changes

Page actions are the words a microflow uses — show page, save changes, cancel changes, close page, create object … then …, delete, open link, sign out, complete task, call microflow M.F, call nanoflow M.F. The same in Action:, OnClick:, OnChange:, named action slots ('createFileAction': …), alter page … set, and a menu item's sign out. Arguments are untouched (#751 owns them).

One spelling per keyword

Canonical (describe emits it)	Old spelling (still parses, warns)	Code
page action words above	show_page, save_changes, cancel_changes, close_page, create_object, delete_object, open_link, sign_out, complete_task, microflow M.F, nanoflow M.F	MDL-DEPR020
error message '…' (after not null / unique / required, in a validation rule, after on delete restrict, disallow concurrent execution)	error '…', feedback '…', error_message, errormessage	MDL-DEPR021
on delete cascade | restrict | set null	delete_behavior … in all its spellings (incl. the three spellings each of delete_and_references etc.), also alter association … set delete_behavior	MDL-DEPR022
ReferenceSet	reference_set	MDL-DEPR023
returns nothing	returns none	MDL-DEPR024

Every alias is marked in the grammar (/* @alias MDL-DEPRnnn */), registered with Example/CanonicalExample (the registry test proves both build the same statements), and has an fmt --upgrade rewrite that keeps the script's letter case. delete_object close_page, which describe could print but the grammar refused, now parses.

Lowercase keywords are canonical; fmt no longer upper-cases names. formatter.Format upper-cased every word on a keyword list, names included (Issue64.User → Issue64.USER, attribute Title → TITLE) and changed what 374 example scripts build. It now lowercases only tokens the parse tree shows are keywords (visitor.FormatSpans), keeping property keys (a keyword followed by :/=), names (anything reached through keyword/identifierOrKeyword/qualifiedName), CamelCase or digit-bearing values (ButtonStyle: Success, RenderMode: H2), data types and annotations. Text stored verbatim (expressions, XPath, OQL, catalog/SQL queries, template params, multi-line literals) keeps case and layout. describe now writes lowercase folder, workflow default ->, and published-REST get/post.

Design choices the ADRs did not settle

• Codes start at MDL-DEPR020, not 006, because R3/R4: one argument-binding form (Param = expr) and alter set ( Key: value ) everywhere (3.1) #751/R5: XPath always in [ ], expressions bare, one constant reference (3.3) #753–R6/R7/R9/R10: verbs, session commands, metadata placement, Studio Pro document names (3.5–3.6) #755 add registry entries in parallel; R8's entries live in their own slice (r8Entries) so the merges do not collide. A gap in the numbering means nothing.
• Two-word actions without their own tokens (save changes, cancel changes, sign out, complete task) are one lexer token admitting both spellings (WS+ or _), like not null; the underscore identifies the alias. Actions whose words are already tokens (show page, close page, create object, open link, call microflow) are token sequences in actionExprV3 — a lexer-level show page would have broken show pages (longest match).
• returns nothing wins over returns none: it is what describe already emitted (as Nothing, now lowercase) and what the docs use.
• ReferenceSet (not reference set): it is the Mendix type name describe writes, a value like Reference, not a keyword phrase.
• fmt case rule: a CamelCase word is left as written, because that is how Mendix writes names and enumeration values; an all-caps or all-lowercase word is a keyword. This makes fmt(describe(x)) a fixed point on PedApp and TestApp.
• Not changed, deliberately:
  • ELSEIF is only a reserved token — no statement accepts it, so there is no second spelling to deprecate.
  • NOT_NULL is a token name; its only spelling is not null.
  • ALLOW_CREATE_CHANGE_LOCALLY's optional underscores are what let the property key AllowCreateChangeLocally: lex; the set allow_create_change_locally = … form belongs to R3/R4: one argument-binding form (Param = expr) and alter set ( Key: value ) everywhere (3.1) #751's alter … set ( Key: value ).
• alter settings now stores the section lowercase in the AST (the executor already lowercased it), so keyword case no longer changes the AST.

Test plan (what I ran)

• make build, make lint (Go + TS) — pass.
• go test ./mdl/visitor/ ./mdl/executor/ ./mdl/upgrade/ ./mdl/formatter/ ./mdl/grammar/ ./mdl/deprecation/ ./mdl/langver/ ./cmd/mxcli/... — pass.
• go test -tags integration ./mdl/roundtrip/ (PedApp + TestApp round trip, allowlists, execute-both upgrade property test, describe: end every statement with ';', never print '/' (#744) #745 terminator test) — pass; no allowlist entries added.
• New tests: TestR8OldSpellingsAreAliases / TestR8PageActionWordsBuildTheirAction (visitor: 30 old/canonical pairs build identical statements, only the old records its code, each with a fix), TestUpgrade_R8Spellings (exact rewrites, case kept, idempotent), TestFormatterKeepsMeaning (replaces TestFormatterChangesMeaning: every mdl-examples script formats to one that builds the same statements, idempotently), TestPedAppDescribeUsesCanonicalSpellings / TestTestAppDescribeUsesCanonicalSpellings (integration: describe emits no R8 alias and no upper-case keyword).
• Revert checks:
  • ExitActionExprV3 stubbed → TestR8OldSpellingsAreAliases fails 9 subtests ("recorded nothing").
  • old formatter/format.go restored → TestFormatterKeepsMeaning fails on 374 scripts.
  • describe folder → FOLDER and save changes → save_changes → TestPedAppDescribeUsesCanonicalSpellings fails (9 folder lines, 4 MDL-DEPR020 uses).
  • The registry test (TestRegistryExamplesRecordTheirCode) failed for all five new codes before the grammar/visitor change.
• Manual: mxcli fmt over a describe dump of every PedApp and TestApp document changes only whitespace; mxcli check / fmt --upgrade on a scratch script with named action slots and SHOW_PAGE.
• Not verified in Studio Pro: every change is a respelling that builds the identical AST (so the identical model); the execute-both property test covers the model side.

Follow-ups

• Action: → OnClick: as the one on-click key (describe still writes Action:; §4 property-key convention).
• Menu items page M.P / microflow M.F → show page / call microflow — waiting on R2: three brackets, three meanings — integration documents, navigation/menus, on error, while (3.4) #754's navigation/menu bracket change to avoid a grammar collision.
• alter entity … set allow_create_change_locally = … → R3/R4: one argument-binding form (Param = expr) and alter set ( Key: value ) everywhere (3.1) #751's set ( AllowCreateChangeLocally: … ).
• TestApp describe still emits the list-operation call forms (MDL-DEPR003/004) under mdl 0 — MDL list operations as one statement per Studio Pro activity; set mandatory under mdl 1 (#733) #737's decision; the new canonical-spelling test checks R8 codes only.

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