FE-702: Walking skeleton — brunch binary + TUI over pi (M0)

[lunelson]

significant spec/plan updates re thinness of layers

tighten the definition of command layer

more refinement around session coordination vs specification and boot

[lunelson]

• FE-744: Document Pi command containment evidence #150
• FE-737: Web shell over the same host (M3) #147
• FE-736: JSONL session viability proof (M2) #146
• FE-735: Mode shell and fixture driver (M1) #144
• FE-702: Walking skeleton — brunch binary + TUI over pi (M0) #142 👈 (View in Graphite)
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PR Summary

Medium Risk
Core boot and durable session/spec invariants depend on Pi JSONL timing and a private _rewriteFile() flush path; mistakes would corrupt bindings or duplicate JSONL, though coverage is strong via coordinator/TUI tests and the store oracle.

Overview
Delivers the M0 walking skeleton: brunch now boots a real pi-backed TUI via runBrunchTui and a WorkspaceSessionCoordinator that owns spec selection, .brunch/ state, Pi session creation under .brunch/sessions/, and exactly one brunch.session_binding per session (including same-spec “new session” and pi replacement sessions), with a store-only runbook checker CLI.

The TUI layer gates on ready | select_spec | needs_human, prompts for a spec when needed, and mounts persistent cwd / spec / phase / chat-mode chrome through an internal pi extension (setWidget above the editor); session open/bind stays out of the TUI adapter (enforced by tests).

Planning/docs move walking-skeleton to done and heavily refine SPEC/PLAN toward elicitation-first transcripts, thin named RPC/projection reads, CommandExecutor as the mutation boundary, and coordinator/chrome decisions—plus new docs/praxis/pi-types.md and a bin/brunch.js entry shim.

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