Adopt the BMAD v6.10 consolidated TOML config layout end-to-end

[pbean]

Umbrella issue. No new requirements of its own — it exists so the three children read as one
adoption rather than three unrelated defects.

The shift

BMAD-METHOD v6.10.0 resolves module config from a consolidated four-layer TOML stack, read by
_bmad/scripts/resolve_config.py (tomllib) in this precedence order:

_bmad/config.toml → _bmad/config.user.toml → _bmad/custom/config.toml → _bmad/custom/config.user.toml

with [modules.bmm] beating [core] on key collision. Help is consolidated at
_bmad/_config/bmad-help.csv plus per-module _bmad/<module>/module-help.csv.

The legacy per-module _bmad/bmm/config.yaml and a root _bmad/module-help.csv are no longer
read by the runtime.

Where bmad-loop still assumes the legacy layout

bmad-loop is on the wrong side of this on both the read and the write path:

• Read — bmadconfig.load_paths (src/bmad_loop/bmadconfig.py:70-72) resolves
  implementation_artifacts / planning_artifacts from _bmad/bmm/config.yaml only. → bmadconfig: read the four-layer central TOML as primary, legacy bmm/config.yaml as fallback #154
• Write — the bmad-loop-setup skill's merge-config.py / merge-help-csv.py write
  _bmad/config.yaml and a root _bmad/module-help.csv: files the runtime never reads. → bmad-loop-setup writes legacy config.yaml/module-help.csv; ignored on BMAD v6.10.0 TOML config layout #258
• Docs — the same skill's docs invoke its PEP 723 scripts with bare python3, which fails on
  the inline-dependency scripts. → bmad-loop-setup docs invoke PEP 723 scripts with python3; merge-config.py fails without uv run #259

The installer regenerates the per-module YAML from the TOML on each install/update, so the two
surfaces normally agree — which is exactly what makes the divergence quiet. A hand-added
custom/config*.toml override desyncs them until the next install, and from that moment the
skill writes specs and the deferred-work ledger where the orchestrator is not looking.

Children

• bmadconfig: read the four-layer central TOML as primary, legacy bmm/config.yaml as fallback #154 — bmadconfig: read the four-layer TOML as primary, legacy YAML as fallback
• bmad-loop-setup writes legacy config.yaml/module-help.csv; ignored on BMAD v6.10.0 TOML config layout #258 — bmad-loop-setup writes legacy config.yaml / module-help.csv
• bmad-loop-setup docs invoke PEP 723 scripts with python3; merge-config.py fails without uv run #259 — bmad-loop-setup docs invoke PEP 723 scripts with python3

Each is independently ship-able; #259 in particular is a small standalone docs fix and should not
wait on the other two.

[coderabbitai]

🔗 Related PRs

#73 - fix(setup): never delete live core BMAD config/manifest (#64) [merged]
#118 - Multiplexer selection: availability-aware defaults + dev-chosen backend (#87) [merged]
#155 - fix(worktree): survive the renderer-era bmad-dev-auto (BMAD-METHOD #2587/#2588) [open]
#283 - fix(validate): accept merged bmad-review, drop unreleased verification-gap requirement (#260) [merged]
#285 - fix(setup): register into the BMAD v6.10 TOML config layout (#258) [open]

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