Initial commit: Theriapolis baseline at port/godot branch point

Captures the pre-Godot-port state of the codebase. This is the rollback
anchor for the Godot port (M0 of theriapolis-rpg-implementation-plan-godot-port.md).
All Phase 0 through Phase 6.5 work is included; Phase 7 is in flight.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Theriapolis.Core/Persistence/SaveMigrations/ISaveMigration.cs

@@ -0,0 +1,13 @@
+namespace Theriapolis.Core.Persistence.SaveMigrations;
+
+/// <summary>
+/// Single-step migration from one schema version to the next. Migrations
+/// chain — Migrations.MigrateUp finds a path from header.Version to
+/// C.SAVE_SCHEMA_VERSION and applies each step in order.
+/// </summary>
+public interface ISaveMigration
+{
+    int FromVersion { get; }
+    int ToVersion   { get; }
+    void Apply(SaveHeader header, SaveBody body);
+}

Theriapolis.Core/Persistence/SaveMigrations/Migrations.cs

@@ -0,0 +1,49 @@
+namespace Theriapolis.Core.Persistence.SaveMigrations;
+
+/// <summary>
+/// Registry + chain runner for SaveBody migrations. Phase 4 is the v4 baseline;
+/// older versions are not supported because nothing earlier shipped. As we
+/// bump the schema in Phase 5+, register migrations here.
+///
+/// The registry seeds itself with every built-in migration on first use, so
+/// callers don't need to remember to <see cref="Register"/> them at startup.
+/// </summary>
+public static class Migrations
+{
+    private static readonly List<ISaveMigration> _registry = new();
+    private static bool _seeded;
+
+    public static void Register(ISaveMigration m)
+    {
+        EnsureSeeded();
+        _registry.Add(m);
+    }
+
+    private static void EnsureSeeded()
+    {
+        if (_seeded) return;
+        _seeded = true;
+        // Built-in migrations registered in version order:
+        _registry.Add(new V5ToV6Migration());
+        _registry.Add(new V6ToV7Migration());
+        _registry.Add(new V7ToV8Migration());
+    }
+
+    /// <summary>
+    /// Walk migrations from header.Version up to C.SAVE_SCHEMA_VERSION. Returns
+    /// false if no chain exists; the caller decides whether to hard-block or
+    /// best-effort the load (see SaveCodec docs).
+    /// </summary>
+    public static bool MigrateUp(SaveHeader header, SaveBody body)
+    {
+        EnsureSeeded();
+        while (header.Version < C.SAVE_SCHEMA_VERSION)
+        {
+            var step = _registry.FirstOrDefault(m => m.FromVersion == header.Version);
+            if (step is null) return false;
+            step.Apply(header, body);
+            header.Version = step.ToVersion;
+        }
+        return header.Version == C.SAVE_SCHEMA_VERSION;
+    }
+}

Theriapolis.Core/Persistence/SaveMigrations/V5ToV6Migration.cs

@@ -0,0 +1,27 @@
+namespace Theriapolis.Core.Persistence.SaveMigrations;
+
+/// <summary>
+/// Phase 6 M2 — additive migration from save schema v5 (Phase 5 ship) to
+/// v6 (Phase 6 reputation core). Non-destructive: every v5 field carries
+/// over unchanged. The new <see cref="SaveBody.ReputationState"/> is
+/// already initialised to a fresh empty <see cref="ReputationSnapshot"/>
+/// by the SaveBody constructor, so this migration just bumps the header
+/// version.
+///
+/// Phase 5's placeholder <see cref="SaveBody.Factions"/> and
+/// <see cref="SaveBody.Reputation"/> dictionaries were never populated
+/// (Phase 5 didn't ship the reputation system), so we don't need to
+/// translate any data — they stay empty and ignored.
+/// </summary>
+public sealed class V5ToV6Migration : ISaveMigration
+{
+    public int FromVersion => 5;
+    public int ToVersion   => 6;
+
+    public void Apply(SaveHeader header, SaveBody body)
+    {
+        // Body fields all default-initialise to empty in SaveBody — the
+        // ReputationState is already a fresh ReputationSnapshot. Phase-5
+        // saves had nothing to translate, so this is a pure version bump.
+    }
+}

Theriapolis.Core/Persistence/SaveMigrations/V6ToV7Migration.cs

@@ -0,0 +1,30 @@
+namespace Theriapolis.Core.Persistence.SaveMigrations;
+
+/// <summary>
+/// Phase 6.5 M0 — additive migration from save schema v6 (Phase 6 ship) to
+/// v7 (Phase 6.5 levelling). Non-destructive: every v6 field carries over
+/// unchanged. The new <see cref="PlayerCharacterState.SubclassId"/>,
+/// <see cref="PlayerCharacterState.LearnedFeatureIds"/>, and
+/// <see cref="PlayerCharacterState.LevelUpHistory"/> default-initialise
+/// to empty values by the constructor, so this migration just bumps the
+/// header version.
+///
+/// Phase-6 saves had no level-up history (every character stayed at level
+/// 1, Xp = 0). On load they continue to be valid level-1 characters; the
+/// player can immediately start earning XP and levelling up under the new
+/// rules.
+/// </summary>
+public sealed class V6ToV7Migration : ISaveMigration
+{
+    public int FromVersion => 6;
+    public int ToVersion   => 7;
+
+    public void Apply(SaveHeader header, SaveBody body)
+    {
+        // No data translation needed. PlayerCharacterState's new fields
+        // (SubclassId, LearnedFeatureIds, LevelUpHistory) default-initialise
+        // to empty in their record, and SaveCodec.ReadCharacter handles
+        // missing-section bytes via the EOS-check pattern Phase 5 already
+        // established. Pure version bump.
+    }
+}

Theriapolis.Core/Persistence/SaveMigrations/V7ToV8Migration.cs

@@ -0,0 +1,27 @@
+namespace Theriapolis.Core.Persistence.SaveMigrations;
+
+/// <summary>
+/// Phase 7 M0 — additive migration from save schema v7 (Phase 6.5 ship) to
+/// v8 (Phase 7 dungeons). Non-destructive: every v7 field carries over
+/// unchanged. Phase 7 reserves three new save sections — anchors, building
+/// deltas, and per-PoI dungeon state — but ships M0 with the version bump
+/// only; the fields default-initialise to empty and a v7 save loads as
+/// "no anchors persisted, no buildings modified, no dungeons visited"
+/// which is the truth for any pre-Phase-7 save.
+///
+/// Subsequent Phase 7 milestones (M1+) will populate these sections;
+/// the migration stays additive throughout.
+/// </summary>
+public sealed class V7ToV8Migration : ISaveMigration
+{
+    public int FromVersion => 7;
+    public int ToVersion   => 8;
+
+    public void Apply(SaveHeader header, SaveBody body)
+    {
+        // No data translation needed. Phase 7's new save sections
+        // (TAG_ANCHORS / TAG_BUILDINGS / TAG_DUNGEONS) default to empty in
+        // SaveBody and SaveCodec uses the established EOS-check pattern
+        // for additive sections. Pure version bump.
+    }
+}