feat: checkpoint compact ordinary source and lossless default preservation

docs/language.html

@@ -2,7 +2,7 @@
 <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
 <head>
 <meta charset="utf-8" />
-<meta name="generator" content="Docutils 0.22.2: https://docutils.sourceforge.io/" />
+<meta name="generator" content="Docutils 0.23: https://docutils.sourceforge.io/" />
 <meta name="viewport" content="width=device-width, initial-scale=1" />
 <title>Arcadia Studio OA / SA Language and Editing Contract</title>
 <style type="text/css">
@@ -806,11 +806,11 @@ references may be omitted and then mean <span class="docutils literal">none</spa
 These omissions are accepted in newly authored source 7, not only in schema-2
 compatibility input. Earlier schema admission of constructors and fields is
 still governed by its version rules.</p>
-<p>Canonical formatting writes the hydrated occurrence references and default
-<span class="docutils literal">message_kind</span>, <span class="docutils literal">reply_to</span> and <span class="docutils literal">values</span> explicitly. An absent
-<span class="docutils literal">operation</span> remains omitted in canonical output. Lossless no-op updates and
-unrelated name edits retain authored omissions; canonical formatting is a
-different operation. An admitted incomplete occurrence can still produce model
+<p>Canonical formatting omits optional occurrence references equal to <span class="docutils literal">none</span>,
+the default Asynchronous <span class="docutils literal">message_kind</span>, empty <span class="docutils literal">values</span>, and absent
+<span class="docutils literal">operation</span>. Required fields of a selected constructor remain present.
+Lossless updates retain unchanged explicit defaults and authored omissions;
+canonical formatting is a different operation. An admitted incomplete occurrence can still produce model
 checks requesting its missing work, exchange, lifeline or referenced scenario.</p>
 <table>
 <caption>Occurrence body constructors</caption>
@@ -1569,29 +1569,40 @@ has no explicit default, and does not convey ownership or deletion of the type.<
 <thead>
 <tr><th class="head"><p>Constructor</p></th>
 <th class="head"><p>Required fields</p></th>
+<th class="head"><p>Optional fields (omission value)</p></th>
 </tr>
 </thead>
 <tbody>
 <tr><td><p>Boolean</p></td>
 <td><p>None</p></td>
+<td><p>None</p></td>
 </tr>
 <tr><td><p>Integer</p></td>
-<td><p><span class="docutils literal">minimum</span>, <span class="docutils literal">maximum</span>: optional signed 64-bit integers</p></td>
+<td><p>None</p></td>
+<td><p><span class="docutils literal">minimum</span>, <span class="docutils literal">maximum</span>: signed 64-bit integers? (none)</p></td>
 </tr>
 <tr><td><p>Real</p></td>
-<td><p><span class="docutils literal">minimum</span>, <span class="docutils literal">maximum</span>: optional finite IEEE-754 binary64 values</p></td>
+<td><p>None</p></td>
+<td><p><span class="docutils literal">minimum</span>, <span class="docutils literal">maximum</span>: finite IEEE-754 binary64 values? (none)</p></td>
 </tr>
 <tr><td><p>String</p></td>
-<td><p><span class="docutils literal">minimum_length</span>: u32; <span class="docutils literal">maximum_length</span>: optional u32</p></td>
+<td><p><span class="docutils literal">minimum_length</span>: u32</p></td>
+<td><p><span class="docutils literal">maximum_length</span>: u32? (none)</p></td>
 </tr>
 <tr><td><p>Enumeration</p></td>
 <td><p><span class="docutils literal">literals</span>: unique nonempty, case-sensitive strings</p></td>
+<td><p>None</p></td>
 </tr>
 <tr><td><p>Record</p></td>
-<td><p><span class="docutils literal">supertype</span>: same-layer Record ref?</p></td>
+<td><p>None</p></td>
+<td><p><span class="docutils literal">supertype</span>: same-layer Record ref? (none)</p></td>
 </tr>
 </tbody>
 </table>
+<p>Optional fields may be absent or explicitly <span class="docutils literal">none</span>. Selected String and
+Enumeration constructors still require <span class="docutils literal">minimum_length</span> and <span class="docutils literal">literals</span>,
+respectively, including zero and an empty list. Selecting a constructor does
+not merge fields from the default String definition. Unknown fields reject.</p>
 <p>Bounds are inclusive and ordered; an absent bound means unbounded within the
 represented numeric domain. Integer comparisons MUST NOT convert to binary64.
 NaN, infinities, overflow and reversed bounds reject. String length counts Unicode
@@ -2439,10 +2450,27 @@ references, placements, artifacts, trace baselines, and ordered occurrences.
 Map order is irrelevant. The writer preserves signed coordinate zero and
 emits decimals that recover the original binary32 value.</p>
 <p>Canonical output uses LF, four-space indentation, explicit identities,
-defaults, and JSON-escaped strings. Elements are emitted in UUID order, then
+and JSON-escaped strings. It omits fields equal to the omission defaults of
+their actual declaration or selected constructor, as specified in the field
+tables. This includes an empty project description. It MUST NOT omit a required
+field merely because its value is zero, false, empty, or <span class="docutils literal">none</span>. Elements are emitted in UUID order, then
 relations; diagrams and their nodes follow, then artifacts, then traces.
 Fields use deterministic name order. Output ends with LF. Alias values come
 from the model, never from regenerating display names.</p>
+<p>Omission is context-sensitive: Scenario uses the source default MixedLegacy;
+BoundaryExchange and CommunicationMean have different orientation defaults;
+state declarations determine their state-kind discriminator. A nonempty or
+whitespace-only description remains exact. Present-empty optional strings or
+collections, unbounded multiplicity versus a finite default, selected operation
+intent, and negative coordinate zero remain distinct values. A nondefault
+geometry record retains all required coordinates or dimensions.</p>
+<p>Only specified optional fields inside selected constructors may be omitted.
+For example, Integer bounds and LegacyPortContract.interface may be absent;
+String.minimum_length, Signal.items, port-contract payload lists, and historical
+snapshot name/description fields remain required. A LegacyPortContract record
+still requires direction. Historical semantic baseline payloads are retained
+without generic empty/default pruning. Compact output MUST preserve every
+persistent model field after parsing, including these distinctions.</p>
 <p>Comments and input whitespace are lexical trivia to the canonical writer.
 Canonical export does not preserve them. The source-project editor and compiler
 preserve authored comments and whitespace on Apply while inserting missing
@@ -2484,11 +2512,19 @@ independent parent and child moves are resolved together. Leading whitespace
 adjusts to the destination scope; other token spelling remains authored.</p>
 <p>Updates MUST NOT canonicalize surviving declarations in full. Header, field and
 nested value positions are derived from the existing syntax parser. Unchanged
-fields retain their exact bytes, including field order, omitted defaults, number
+fields retain their exact bytes, including field order, explicit and omitted defaults, number
 and string spelling, comments, indentation and line endings. Changed literals and
 references replace only the required tokens; a reference with comments between
-<span class="docutils literal">&#64;</span> and its alias retains those comments. A previously omitted default is
-inserted only if its semantic value changes. New fields use the existing record's
+<span class="docutils literal">&#64;</span> and its alias retains those comments. A previously omitted field is
+inserted only when needed to express the requested value in its new declaration
+context. This includes an unchanged value whose omission default changes with
+the declaration kind. For example, changing BoundaryExchange to CommunicationMean
+while retaining orientation true requires <span class="docutils literal">oriented true;</span> if previously
+implicit. Unchanged explicit defaults MUST survive unrelated sibling edits,
+including persistence-serializer omissions such as <span class="docutils literal">operation none</span>,
+<span class="docutils literal">port_anchors []</span> and <span class="docutils literal">baseline.semantic none</span>. New fields and value fragments
+use compact generation while retaining required selected-constructor payloads.
+New fields use the existing record's
 indentation and line-ending style without reformatting its other fields.</p>
 <p>A constructor tag change retains shared nested fields in place. Removed fields,
 constructors and declarations remove syntax tokens, retaining their comments
@@ -2770,8 +2806,9 @@ This compatibility applies equally to source and JSON. It adds explicit
 defaults without changing any prior identity, name, reference, order, geometry,
 artifact or trace field. The original V2 golden source/JSON in
 <span class="docutils literal"><span class="pre">crates/oa-core/tests/fixtures</span></span> MUST NOT be regenerated from the newer demo;
-they verify that every old persistent field survives. Canonical output writes
-the added defaults through explicit migration to the current schema 7.</p>
+they verify that every old persistent field survives. Canonical output uses
+the current schema 7 and omits values equal to its specified source defaults;
+parsing recovers the complete migrated model.</p>
 <p>The V2 adapter preserves every original identity, alias, prose, parent,
 placement, trace and artifact. Generic ports become Legacy with their original
 direction/interface record. Existing FE endpoint IDs remain unchanged. For