feat(vpc): binary .vpb stub companion and str->char* migration in call gen

- add VpiStub: fixed-layout blob written next to every .vpi (dual write at all
  writers, Ensure() backfills a missing or stale companion on cache reuse)
- serve arity/signature queries for top-level functions from the blob, with a
  silent fallback to the text scanner (methods, varargs, duplicates, corrupt file)
- prefer the injected declare over the text arity in the cross-module check
- CDefine/type text indexes and in-place SSA renumbering and bulk appends
- WIP: char* conversion in CallGenBase and CallGenLeafKit

Tools/lsp/fixtures/gate10_use.vp

@@ -98,6 +98,19 @@ def string_use() -> int:
     return len("hello")
 
 
+def negative_use() -> int:
+    return -128
+
+
+def negative_float_use() -> float:
+    return -3.5
+
+
+def subtract_use() -> int:
+    x: int = 5
+    return x - 1
+
+
 def else_block(flag: int) -> int:
     if flag != 0:
         return 1

Tools/lsp/probe.py

@@ -1885,6 +1885,20 @@ def gate10(exe: str) -> int:
     for piece in ("type     str", "length   5 bytes"):
         if piece not in string_hover:
             raise AssertionError(f"string hover lacks {piece!r}: {string_hover}")
+    neg_hover = hover_text(at("return -128", len("return -")))
+    for piece in ("dec      -128", "hex      -0x80", "binary   -0b1000_0000",
+                  "bits     8 signed", "uint     n/a (negative)", "int      i8",
+                  "float    f16 exact, f32 exact, f64 exact"):
+        if piece not in neg_hover:
+            raise AssertionError(f"negative hover lacks {piece!r}: {neg_hover}")
+    neg_float_hover = hover_text(at("return -3.5", len("return -")))
+    if "hex      0xC00C000000000000" not in neg_float_hover:
+        raise AssertionError(f"negative float bit pattern is wrong: {neg_float_hover}")
+    if "f16 exact, f32 exact, f64 exact" not in neg_float_hover:
+        raise AssertionError(f"negative float exactness is wrong: {neg_float_hover}")
+    minus_hover = hover_text(at("return x - 1", len("return x - ")))
+    if "dec      1" not in minus_hover:
+        raise AssertionError(f"binary minus was treated as unary: {minus_hover}")
 
     def reference_ranges(pos: dict[str, int]) -> list[tuple[str, int, int]]:
         result = request("textDocument/references", pos,