feat: updated the text reflow engine

gateway/app/routers/edits.py

@@ -228,6 +228,9 @@ class ReflowRun(BaseModel):
     internalFontId: str
     fontSize: float
     color: str = "#000000"
+    # Original per-character advance (PDF units) of UNCHANGED source text, for pixel-perfect
+    # reflow spacing. Omitted for edited/new runs (engine re-measures those).
+    advances: list[float] | None = None
 
 
 class ReflowParagraphData(BaseModel):
@@ -241,6 +244,10 @@ class ReflowParagraphData(BaseModel):
     align: Literal["left", "justify"] = "left"
     pushColumnLeft: float | None = None
     lines: list[list[ReflowRun]] | None = None
+    # Original per-line baseline + left anchor (parallel to `lines`), so unchanged lines reproduce
+    # the source's exact vertical spacing and left edge instead of a uniform fallback.
+    lineBaselineY: list[float] | None = None
+    lineX: list[float] | None = None
 
 
 class ReflowParagraphOperation(BaseModel):