Write the v3.0 migration guide for consuming projects and forks

[braboj]

Context

templates/base/core/docs.md MUSTs docs/PLAYBOOK.md and docs/ONBOARDING.md
as standard documents, and base/core/docs.md resolves into 17 of 17 chains.
Every project generated from these templates therefore carries those filenames.

#1291 decides whether those names change — the noun (playbook vs runbook)
and the casing (SHOUT-case vs kebab-case). This issue carries the rollout, so
that the decision and its downstream cost are tracked separately.

Blocked on #1291. Nothing here is actionable until the noun and the casing
are settled. If #1291 concludes "keep the names as they are", close this as
wontdo.

Affected repositories (surveyed 2026-08-30)

Measured from the git tree of each repository's default branch across both
accounts. 14 repositories carry docs/PLAYBOOK.md — this one and 13 consumers.

• braboj/corrosim — PLAYBOOK, ONBOARDING
• braboj/coinsift — PLAYBOOK, ONBOARDING
• braboj/demo-randomgen — PLAYBOOK, ONBOARDING
• braboj/demo-sensor-app — PLAYBOOK, ONBOARDING
• braboj/page-fetcher — PLAYBOOK, ONBOARDING
• braboj/tutorial-git — PLAYBOOK, ONBOARDING
• braboj/wuseria — PLAYBOOK, ONBOARDING
• braboj/braboj.github.io — PLAYBOOK, ONBOARDING
• Imbra-Ltd/pyomb — PLAYBOOK, ONBOARDING
• Imbra-Ltd/protocol-modbus — PLAYBOOK, ONBOARDING
• Imbra-Ltd/protocol-devicenet — PLAYBOOK, ONBOARDING
• Imbra-Ltd/nango-blogs — PLAYBOOK, ONBOARDING
• Imbra-Ltd/imbra-io.github.io — PLAYBOOK only

Only braboj/solid-ai-templates carries docs/SPEC.md, so a SPEC.md
decision needs no downstream migration.

Both accounts have the same owner, so no third party is affected. Each
repository still needs its own pull request under its own branch protection.

Cost

Measured on the two local clones: braboj/corrosim holds 54
PLAYBOOK/ONBOARDING mentions across 6 tracked files, Imbra-Ltd/coinsift
49 across 5. Extrapolated, the 13 consumers hold roughly 650 mentions across
~70 files, against 254 in this repository — so about three quarters of the
work is downstream, and none of it is regenerated by tools/sync.py.

Per-repository steps

1. git mv the affected files under docs/
2. Rewrite references in CLAUDE.md, README.md, CONTRIBUTING.md,
   docs/ONBOARDING.md, docs/dev-journal.md and the renamed files themselves
3. Regenerate the context file if the project is generated per ADR-016, rather
   than hand-editing it
4. Check for links from outside the repository — a published site under
   *.github.io may link the old path, and a moved file breaks it silently

Prerequisite — label taxonomy is not uniform

Several consumers do not carry this repository's issue taxonomy.
braboj/corrosim has no P0–P3 and no task label; Imbra-Ltd/pyomb and
braboj/page-fetcher do. Provision labels in the repositories that lack them
before filing per-repository issues, or track the rollout entirely from the
checklist above.

Hazard for a scripted migration

core.autocrlf=true is set on the development machine, so any script that
reads a working copy and writes it back commits CRLF line endings — a 7-line
change once landed as a 451-line diff here and passed review, CI and every
gate. A migration script MUST read as bytes, normalise CRLF to LF and strip
stray lone CR characters, then write. A fix that only collapses CRLF pairs
leaves a doubled CR intact.

Open question for #1291 to answer

Whether existing projects migrate at all. The alternative is that generated
projects keep the filenames they were created with, and only newly generated
ones use the new name — which costs nothing here but leaves the estate
permanently split. #1291 should state which, because the two answers produce
completely different work.

[braboj]

Unmilestoned at the 2026-09-03 groom. Conditional work, milestoned as
planned.

This migrates 13 consuming repositories once the guide-doc names are decided.
The decision is #1291 and it is open, so there is nothing to migrate to.

Trigger: #1291 lands a decision that renames at least one guide doc. If it
resolves by keeping the filenames and fixing the description -- the third
answer its body offers -- close this as no longer applicable.

[braboj]

Milestoned v3.0 at the 2026-09-08 groom, for the same reason as its blocker: this is the rollout of #1291's decision and #1291 is milestoned v3.0. If #1291 concludes the names stay, close this wontdo at that point rather than carrying it through the cut.

[braboj]

Rescoped for v3.0: the guide-doc rename becomes one part of the v3.0 migration guide, which tells projects and forks how to re-pin, the -s ours step, and the manifest ownership rule. The guide-doc filename decision stays with #1291.

[braboj]

Unblocked by the decision in #1291 (ADR-047, PR #1865): every file under docs/ becomes kebab-case (onboarding.md, playbook.md, spec.md), and the noun stays playbook. The open question here is answered: existing projects do migrate, but each one when it moves to v3.0, renaming all three files in that change — not as a campaign ahead of the release. The guide should therefore carry the three git mv commands and the reference rewrite as a step of the v3.0 upgrade, and the checklist above is ticked as each repository upgrades.

[braboj]

The v3.0 migration now also carries #1872: ONBOARDING merges into CONTRIBUTING (so onboarding.md is folded in rather than renamed as ADR-047 states), README drops Project structure and Development setup, and the development journal gives way to docs/lessons.md (#1870, ADR-048). The guide should present all three as one migration step.