docs(adr): ADR-066 — abstract hierarchy vocabulary (peat#904 Phase 0)

[kitplummer]

Summary

Phase 0 of the peat#904 workspace-wide rename epic. Docs-only. Establishes:

• Vocabulary mapping (4 tiers): Squad → Cell (consolidates the existing Cell concept), Platoon → Cohort, Company → Federation, plus a new Coalition tier (no military rename — newly-added tier 4). Platform unchanged.
• Why Coalition is in scope now: a concrete deployment (US Army echelon scaling to 1000+ peers) needs a 4th tier today. Shipping Phase 1 without it would force a second wire-format break immediately after.
• Why this vocabulary: domain-neutral (no single field — military, biology, K8s, civic, transport — owns these terms); K8s-collision-free (unlike Pod/Cluster/Fleet, which directionally conflict with K8s's containment + cardinality model); preserves the half-done Cell consolidation work; Federation and Coalition both carry semantic information about peat's actual coordination model (autonomous parties combining for action).
• Hard limit at 4 tiers: tier 5+ (Brigade/Division/Corps scale, ~10000+ peers) is explicitly out of scope under this rigid-schema design. Planned ADR-067 (parametric N-tier aggregation) will lift the limit when a tier-5 deployment becomes concrete — generic AggregationSummary proto with level: uint32 + parent_level_id, tier names become deployment-config labels rather than schema types. ADR-067 is planned but not yet in flight.
• Field/document-key/event renames + Coalition additions: full table in the ADR. squad_id→cell_id (consolidates), platoon_id→cohort_id, company_id→federation_id, new coalition_id. SquadSummary→CellSummary, etc., new CoalitionSummary. HierarchyLevel::{Squad,Platoon,Company}→::{Cell,Cohort,Federation}, new ::Coalition.
• Wire-format strategy: hard rename + peat-schema major version bump. No deprecated aliases. Justified by pre-1.0 posture + revealed preference for clean cuts (peat#898, peat#704).
• CoT/TAK boundary translation: external CoT type strings (a-f-G-U-C-I) are wire artifacts and may appear in peat-transport/src/tak/bridge/; internal types translated to the new vocabulary at the boundary.
• Phase sequence: Phase 1 peat-schema (rename + add CoalitionSummary), Phase 2 peat-protocol (rename + implement Coalition aggregation), Phase 3 peat-mesh (rename + extend hierarchy strategies for Coalition tier), Phase 4 peat-transport TAK bridge + CI grep gate. Phases 1–3 are no longer pure renames — they also add the Coalition tier's new code paths. One PR per repo per the ecosystem skill.

This PR is intentionally draft so the vocabulary + tier-count can be redirected before downstream phases consume it. Phases 1–4 are blocked on this ADR's acceptance.

Revision history

• First push: proposed organismal biology (Cell → Tissue → Organ). Rejected on review as too scientific.
• Second push: switched to Cell → Cohort → Federation — topology-spirit, K8s-collision-free, fully domain-neutral.
• Third push (current): added Coalition as tier 4 (concrete 1000+-peer deployment driving the need) + ADR-067 placeholder for tier 5+ parametric model.

Test plan

• ADR follows the established format
• No code changes; docs-only — no CI build/test gates apply beyond ADR formatting
• Kit confirms or redirects the Cell → Cohort → Federation → Coalition 4-tier mapping
• Kit confirms the hard-rename + major-version-bump approach vs. deprecated-alias migration
• Kit gives green light on a separate tracking issue for ADR-067 (parametric N-tier)
• On accept, this ADR moves to Status: Accepted and Phase 1 PR opens against peat-schema

Tracks peat#904.

[github-actions]

Peat QA Review (SHA: c5f9746)

Scope: Docs-only ADR (Phase 0 of peat#904). No code changes; security-primitive, FFI/BLE, peat-mesh transport, and test-surface checks do not apply to this PR.

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[WARNING] Verification grep gate — command is syntactically broken

The "Verification gate" section specifies:

```bash
grep -rEln '\b(Squad|Platoon|Company|Battalion|Regiment|Brigade|Division|Fireteam)\w*'
--include='.rs' --include='.proto'
-- ':!docs/adr' ':!docs/whitepaper' ':!CHANGELOG.md' ':!CLAUDE.md' ':!SKILL.md'
-- ':!/tests/fixtures/' ':!peat-transport/src/tak/bridge/**'
```

POSIX grep does not interpret :!pattern git-pathspec exclusion syntax. After --, those tokens are treated as literal file paths to search — no file named :!docs/adr exists, so grep finds no input files, returns exit 1 (or 0 with GNU grep and no matches), and the "empty output" acceptance criterion is satisfied regardless of actual codebase content. The gate silently passes even when violations are present.

Action: Replace grep with git grep, which natively supports :! pathspecs:

```bash
git grep -Eln --perl-regexp '\b(Squad|Platoon|Company|Battalion|Regiment|Brigade|Division|Fireteam)\w*'
-- '.rs' '.proto'
':!docs/adr' ':!docs/whitepaper' ':!CHANGELOG.md' ':!CLAUDE.md' ':!SKILL.md'
':!/tests/fixtures/' ':!peat-transport/src/tak/bridge/**'
```

Or, if CI runs outside a git worktree, replace each exclusion with --exclude-dir / --exclude flags. The ADR's own acceptance criterion must be executable and correct before Phase 4 ships.

---

[WARNING] Tier vocabulary table conflates renames with new additions

The top-level tier table uses an identical "Old (military) → New (abstract)" row format for both existing-code renames (Squad→Cell, Platoon→Cohort, Company→Federation) and for Coalition, which is a new tier addition with no existing implementation. A Phase 1 implementer reading the tier table in isolation would look for a HierarchyLevel::Battalion variant or battalion_id field to rename — neither exists in the current codebase. The field-name renames table correctly marks coalition_id and CoalitionSummary as "(new — no military analogue used in code)", but the tier table's "New tier in this ADR" annotation is in the Meaning column where it can be skimmed past.

Action: Visually separate renames from additions in the tier table — e.g., a "+" prefix on the Coalition row's Old column, a dedicated "New tiers added by this ADR" sub-table beneath the rename table, or a column annotation. The goal is that Phase 1's implementer cannot mistake Coalition for a rename when reading the authoritative ADR table.