The graphs a release opt will actually print, drawn inline

[tamnd]

opt carries six dot printers that a release build keeps: dot-cfg,
dot-cfg-only, dot-dom, dot-post-dom, dot-ddg and dot-callgraph.
This reads what they emit and draws it, so the picture in a lesson is
LLVM's graph rather than one reconstructed from the IR alongside it.

m = irx.compile_c(src, opt="-O1")
irx.cfg(m)          # blocks with their instructions, T/F on the arms
irx.cfg(m, bodies=False)
irx.dom(m)          # and irx.graph(m, "post-dom")
irx.ddg(m)
irx.callgraph(m)

A Graph prints as text in a plain terminal, renders as an inline SVG in
a notebook, and exposes .nodes, .edges, .loops and .successors()
for a lesson that wants to assert on the shape rather than show it.

It is not a SelectionDAG viewer

-view-isel-dags and that whole family are declared inside #ifndef NDEBUG; the #else branch supplies static const bool ViewDAGCombine1 = false, .... On a release toolchain the flag is not turned off, it is not
a flag at all, and opt/llc reject it
(llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp:147-189@llvmorg-23.1.0).
The book pins a release build, so no lesson can use them. The data
dependence graph is the graph a release opt gives you that genuinely is
a DAG, cycles and all collapsed into pi-blocks, and it is here as
irx.ddg.

Notes

• No Graphviz. Layout is a longest-path ranking with lanes for back
  edges and for forward edges that skip a row, which is enough for the
  block counts a lesson shows and keeps the install to nothing.
• Stable bytes. LLVM names nodes after object addresses, so printing
  the same function twice gives two different files. The parser maps them
  to n0, n1, ... and the one generated id in the SVG is a content
  hash, so rebuilding a notebook does not produce a diff.
• No script, no click handlers. It ends up in saved notebooks and in
  static site HTML.
• proc.run grows a cwd parameter: the printers write into the working
  directory and there is no flag that redirects them.

Checks

• toolkit: 209 tests, OK (26 new, 8 of them against a real LLVM)
• repo: 98 tests, OK
• ruff check ., build.py check, prosecheck, refcheck --ledger,
  build.py diagrams clean

Part of #10.