feat(m6a): add file save acceptance smoke

[Change Nature]
This commit adds the bounded M6a file-save acceptance path.

[New Capability]
- Add file-level round-trip and deterministic continuation coverage.
- Add Headless --m6a-smoke with digest checks and explicit PASS/FAIL output.

[Implementation]
- Reject non-finite numeric values and negative inventory quantities.
- Exercise dialogue, chat/rumor, trade, events, annals, time, and RNG state.

[Impact]
- Affects Kernel save parsing, Kernel tests, and Headless smoke tooling.
- Preserves the existing save format and M5 smoke behavior.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/LivingVillage.Kernel/WorldSave.fs b/src/LivingVillage.Kernel/WorldSave.fs
index 726170b..8a47c7d 100644
--- a/src/LivingVillage.Kernel/WorldSave.fs
+++ b/src/LivingVillage.Kernel/WorldSave.fs
@@ -72,13 +72,13 @@ module WorldSave =
     let private readFloat (reader: TokenReader) label =
         let token = reader.Take(label)
         match Double.TryParse(token, NumberStyles.Float, invariant) with
-        | true, value -> value
+        | true, value when not (Double.IsNaN(value) || Double.IsInfinity(value)) -> value
         | _ -> invalid (sprintf "invalid %s" label)
 
     let private readFloat32 (reader: TokenReader) label =
         let token = reader.Take(label)
         match Single.TryParse(token, NumberStyles.Float, invariant) with
-        | true, value -> value
+        | true, value when not (Single.IsNaN(value) || Single.IsInfinity(value)) -> value
         | _ -> invalid (sprintf "invalid %s" label)
 
     let private readBool (reader: TokenReader) label =
@@ -450,6 +450,8 @@ module WorldSave =
         [ for index in 0 .. count - 1 do
               let item = readItemKind reader (sprintf "%s[%d].item" label index)
               let quantity = readInt reader (sprintf "%s[%d].quantity" label index)
+              if quantity < 0 then
+                  invalid (sprintf "invalid %s[%d].quantity" label index)
               yield item, quantity ]
         |> Map.ofList