Operating manual for the Lineth Stack quickstart — the Docker-Compose dev/demo stack at docs/getting-started/lineth-stack in the lineth-monorepo that boots a local Linea/Lineth L2 with Sepolia or local L1 finality. Use whenever you are working inside the lineth-stack quickstart and need to boot or run the stack, choose between local and Sepolia L1 mode, get past the Sepolia deployer-funding step, read the finality/success signals, run traffic or bridge smoke tests, reset it, or debug a failing boot (L1 RPC unreachable, deploy gas too low, unfunded deployer, port collision, prover out-of-memory, address mismatch, finality not advancing). Trigger even on casual asks — "start the stack", "run the quickstart", "boot lineth locally", "my deploy keeps failing", "finality isn't happening", "reset the quickstart". When editing this package's scripts or docs, also read rules/making-changes.md so commits pass the repo's lint and DCO gates.