diff --git a/provider/src/pacta_provider/webdocs.py b/provider/src/pacta_provider/webdocs.py
index 7a9f017..634b5a0 100644
--- a/provider/src/pacta_provider/webdocs.py
+++ b/provider/src/pacta_provider/webdocs.py
@@ -50,6 +50,13 @@ def _leaf_ok(entry: LogEntry) -> bool:
     )
 
 
+def _leaf_short(component: str) -> str:
+    """Compact display name for a leaf box at small spans."""
+    return (component.replace("-ed25519-verified", "")
+            .replace("ltl-accumulator-verified", "accum")
+            .replace("fips205-slhdsa-verified", "slh-dsa"))
+
+
 def _svg_tree(entries: list[LogEntry], root_hex: str, signing_backend: str, head_label: str = "Ed25519") -> str:
     """The accumulator, drawn from its real leaves."""
     if not entries:
@@ -77,12 +84,22 @@ def _svg_tree(entries: list[LogEntry], root_hex: str, signing_backend: str, head
                 ok = _leaf_ok(entry)
                 component = (((entry.leaf.get("attestation") or {}).get("subject")) or {}).get("component", "?")
                 fill, stroke = ("#e2f2e9", "#1e7f4f") if ok else ("#f4f4f6", "#8a93a0")
-                out.append(f'<rect x="{x-56}" y="{y-22}" width="112" height="44" rx="5" fill="{fill}" stroke="{stroke}" stroke-width="1.4"/>')
-                out.append(f'<text x="{x}" y="{y-6}" text-anchor="middle" fill="#333">leaf {node_index}</text>')
-                short = escape(str(component).replace("-ed25519-verified", ""))
+                # Boxes must FIT the per-leaf span at any tree size (the
+                # 2026-08-16 lesson: fixed 112px boxes shingled at 19
+                # leaves). Rich boxes while they fit, compact ones after.
+                box_w = min(112.0, span * 0.94)
+                compact = box_w < 100
+                short = escape(_leaf_short(str(component)))
                 label = short if ok else f"{short} ✗"
-                out.append(f'<text x="{x}" y="{y+8}" text-anchor="middle" fill="{stroke}">{label}</text>')
-                out.append(f'<text x="{x}" y="{y+19}" text-anchor="middle" fill="#999" font-size="9">{node.hex()[:10]}…</text>')
+                if compact:
+                    out.append(f'<rect x="{x-box_w/2:.1f}" y="{y-18}" width="{box_w:.1f}" height="36" rx="4" fill="{fill}" stroke="{stroke}" stroke-width="1.2"/>')
+                    out.append(f'<text x="{x}" y="{y-4}" text-anchor="middle" fill="#333" font-size="8">leaf {node_index}</text>')
+                    out.append(f'<text x="{x}" y="{y+9}" text-anchor="middle" fill="{stroke}" font-size="7">{label}</text>')
+                else:
+                    out.append(f'<rect x="{x-box_w/2:.1f}" y="{y-22}" width="{box_w:.1f}" height="44" rx="5" fill="{fill}" stroke="{stroke}" stroke-width="1.4"/>')
+                    out.append(f'<text x="{x}" y="{y-6}" text-anchor="middle" fill="#333">leaf {node_index}</text>')
+                    out.append(f'<text x="{x}" y="{y+8}" text-anchor="middle" fill="{stroke}">{label}</text>')
+                    out.append(f'<text x="{x}" y="{y+19}" text-anchor="middle" fill="#999" font-size="9">{node.hex()[:10]}…</text>')
             else:
                 is_root = level_index == len(levels) - 1
                 out.append(f'<rect x="{x-50}" y="{y-15}" width="100" height="30" rx="5" fill="{"#eef0f7" if is_root else "#fff"}" stroke="{"#3b4d8f" if is_root else "#bbb"}" stroke-width="{1.6 if is_root else 1}"/>')
@@ -91,11 +108,19 @@ def _svg_tree(entries: list[LogEntry], root_hex: str, signing_backend: str, head
                 for child in (2 * node_index, 2 * node_index + 1):
                     if (level_index - 1, child) in positions:
                         cx, cy = positions[(level_index - 1, child)]
-                        out.append(f'<line x1="{x}" y1="{y+15}" x2="{cx}" y2="{cy-22 if level_index==1 else cy-15}" stroke="#ccc"/>')
+                        leaf_top = 18 if len(entries) > 9 else 22
+                        out.append(f'<line x1="{x}" y1="{y+15}" x2="{cx}" y2="{cy-leaf_top if level_index==1 else cy-15}" stroke="#ccc"/>')
     root_x, root_y = positions[(len(levels) - 1, 0)]
-    out.append(f'<rect x="{root_x-190}" y="{root_y-72}" width="380" height="34" rx="6" fill="#e2f2e9" stroke="#1e7f4f" stroke-width="1.6"/>')
-    out.append(f'<text x="{root_x}" y="{root_y-58}" text-anchor="middle" fill="#1e7f4f" font-weight="bold">Signed Tree Head — {escape(head_label)}({root_hex[:12]}…)</text>')
-    out.append(f'<text x="{root_x}" y="{root_y-46}" text-anchor="middle" fill="#1e7f4f" font-size="9">signed by: {escape(signing_backend)} (verify path attested; signing itself not proven)</text>')
+    # The head box sizes itself to its longest line (the 2026-08-16
+    # lesson: a fixed 380px box let a growing caption spill both sides).
+    title = f"Signed Tree Head — {head_label}({root_hex[:12]}…)"
+    line2 = f"signed by: {signing_backend}"
+    line3 = "(verify path attested; signing itself not proven)"
+    head_w = max(len(title) * 7.0, len(line2) * 5.3, len(line3) * 5.3) + 28
+    out.append(f'<rect x="{root_x-head_w/2:.1f}" y="{root_y-84}" width="{head_w:.1f}" height="46" rx="6" fill="#e2f2e9" stroke="#1e7f4f" stroke-width="1.6"/>')
+    out.append(f'<text x="{root_x}" y="{root_y-70}" text-anchor="middle" fill="#1e7f4f" font-weight="bold">{escape(title)}</text>')
+    out.append(f'<text x="{root_x}" y="{root_y-58}" text-anchor="middle" fill="#1e7f4f" font-size="9">{escape(line2)}</text>')
+    out.append(f'<text x="{root_x}" y="{root_y-47}" text-anchor="middle" fill="#1e7f4f" font-size="9">{escape(line3)}</text>')
     out.append(f'<line x1="{root_x}" y1="{root_y-38}" x2="{root_x}" y2="{root_y-15}" stroke="#1e7f4f" stroke-width="1.4"/>')
     out.append("</svg>")
     return "".join(out)
diff --git a/tests/test_web_and_witness.py b/tests/test_web_and_witness.py
index 27870a5..0c18907 100644
--- a/tests/test_web_and_witness.py
+++ b/tests/test_web_and_witness.py
@@ -181,3 +181,32 @@ def test_webdocs_source_carries_no_stale_paper_claims():
     # first-use glosses the page promised: STH and axiom cones
     assert "Signed Tree Head (STH)" in text
     assert "axiom cones (the exact set of assumptions" in text
+
+
+def test_svg_tree_boxes_never_overlap_or_spill():
+    # Regression for 2026-08-16: fixed-width leaf boxes shingled once the
+    # log outgrew the 8-leaf design, and a fixed head box let its caption
+    # spill. Render the tree at several sizes and assert geometry.
+    import re
+
+    from pacta_provider.webdocs import _svg_tree
+
+    class _E:
+        def __init__(self, i):
+            self.leaf_hash = f"{i:02x}" * 32
+            self.leaf = {"attestation": {"subject": {"component": "betrusted-ed25519-verified"},
+                                         "certificates": [{"status": "proven", "axiom_status": "clean"}]}}
+
+    for n in (8, 19, 33):
+        svg = _svg_tree([_E(i) for i in range(n)], "ab" * 32, "verified-dalek-serial")
+        rects = [(float(m.group(1)), float(m.group(2)), float(m.group(3)))
+                 for m in re.finditer(r'<rect x="([-0-9.]+)" y="([0-9.]+)" width="([0-9.]+)"', svg)]
+        leaf_y = max(y for _, y, _ in rects)
+        leaves = sorted((x, w) for x, y, w in rects if y == leaf_y)
+        assert len(leaves) == n
+        for (x1, w1), (x2, _w2) in zip(leaves, leaves[1:]):
+            assert x1 + w1 <= x2 + 0.01, f"leaf boxes overlap at n={n}"
+        # head caption must fit its box: longest line estimated at 5.3px/char
+        head = re.search(r'<rect x="[-0-9.]+" y="[0-9.]+" width="([0-9.]+)" height="46"', svg)
+        title = re.search(r'font-weight="bold">([^<]+)</text>', svg).group(1)
+        assert len(title) * 7.0 <= float(head.group(1)), "head title spills"