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docs(r11): embedded Lua policy engine — example 42 + chapter 42 (Deep Dives) - #11
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… Dives) Part 12 opens: pmon lifts its restart/backoff decision out of the compiled host and into a single shared policy.lua, embedded three structurally different ways — C++23 via sol2 (Lua 5.4), Go via gopher-lua (Lua 5.1), Rust via mlua (Lua 5.4) — and hot-reloaded live on a real SIGHUP with no process restart. Example 42-embedded-lua-scripting (mode: local): - one Lua-5.1-safe policy.lua drives all three hosts to byte-identical decisions (diff-confirmed); policy-v2 is the SIGHUP edit (500ms→100ms backoff, max_restarts 8→2 flipping a restart into an escalate). - sandbox opens only base/string/table/math, nils the loader globals, and never loads os/io/package/debug; policy-evil.lua (os.execute) and policy-broken.lua (missing end) prove runtime + load-time rejection, with genuinely different diagnostics per binding. - verify.lua asserts behaviour (PASS 19/FAIL 0 per language), not exit codes. Chapter 42 to the spine: Tools-used box, 3 verbatim tri-language codetab sets, Figures 42.1 (host↔script boundary) + 42.2 (SIGHUP reload lifecycle), verified footer. validate.py: teach check_lua to skip fixtures declaring "validate: expect-syntax-error" (policy-broken.lua is invalid by design). Gate: test-all-examples.py --only 42 → 3 passed/0 failed; full --mode local → 96 passed/0 failed/3 skipped (skips are 38-otel, lgtm down). validate: OK.
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Part 12 (Deep Dives) opens.
pmonlifts its restart/backoff decision out of the compiled host and into a single sharedpolicy.lua, embedded three structurally different ways — C++23 via sol2 (Lua 5.4), Go via gopher-lua (Lua 5.1), Rust via mlua (Lua 5.4) — and hot-reloaded live on a real SIGHUP with no process restart.Example
42-embedded-lua-scripting(mode: local)policy.luadrives all three hosts to byte-identical decisions (diff-confirmed).policy-v2.luais the SIGHUP edit: 500ms→100ms base backoff,max_restarts8→2, flipping a would-be restart into an escalate.base/string/table/math, nils the loader globals, never loadsos/io/package/debug.policy-evil.lua(os.execute) andpolicy-broken.lua(missingend) prove runtime + load-time rejection — with genuinely different diagnostics per binding (sol2/mlua name the nil global via PUC-Lua; gopher-lua's guard table names the blocked field).verify.luaasserts behaviour (PASS 19 / FAIL 0 per language), not exit codes.Chapter 42
To the spine (Part "Deep Dives"): Tools-used box, 3 verbatim tri-language codetab sets, Figures 42.1 (host↔script boundary) + 42.2 (SIGHUP reload lifecycle), verified footer.
Tooling
validate.pynow skips.luafixtures declaringvalidate: expect-syntax-error(policy-broken.luais invalid by design).Gate
test-all-examples.py --only 42-embedded-lua-scripting→ 3 passed / 0 failed--mode local→ 96 passed / 0 failed / 3 skipped (skips are38-otel, lgtm down)validate.py: OKLibraries:
sol2/3.5.0+lua/5.4.6(Conan),gopher-lua v1.1.2,mlua 0.12(lua54+vendored).