Slice E: relationship mutation (remove_relationship / update_relationship)

[david-w-t]

Slice E — Relationship mutation (remove_relationship / update_relationship)

Completes the connection-arc write-path: the exact mirror of add_relationship,
plus per-direction AVP editing. Connection-arcs only — these never touch the
parents/classes caches, so there is no cache work.

What's added

API	Behaviour
remove_relationship/3,4	Atomically deletes both directed rows of a logical connection edge
update_relationship/4,5	AVP-only edit of the single directed row named by (S, C, T)
update_relationship_both/4,5	Edits both directions with independent {Fwd, Rev} lists
mutate/1	Three new batch grammar kinds wiring the above (with/without template)

Key design points

• Remove is edge-level; AVP update is directed-row-level. The (S, C, T)
  triple names one directed row — name (T, R, S) to edit the reverse. Removal
  always takes both rows (a half-edge is invalid); a missing symmetric partner
  aborts {dangling_half_edge, Id} before any delete.
• Ambiguity contract. Nothing dedups connection edges at write time, so a key
  matching more than one logical edge → {ambiguous_relationship, Templates}
  (templates carried so a /3 caller can re-issue as /4); zero matches →
  relationship_not_found.
• ?ARC_TEMPLATE is protected from edit in both directions (changing scope is
  a structural rewire, not metadata).
• Reuses slice B's validate_avp_updates/1 + apply_avp_updates/2 unchanged.
  One tier-1 update primitive; *_both is pure composition above it.
• Transaction-seam compliant: tier-1 in-txn primitives are gen_server-free and
  never open their own transaction; tier-2 own one transaction/1; tier-3
  (mutate/1) composes tier-1 directly.

Scope / deferred (recorded in TASKS.md)

Structural rewiring (characterization/target_nref/reciprocal — expressible
as mutate([remove, add])) and a rel-id-keyed form (the only disambiguator for a
genuine duplicate edge) are deferred. Compositional-arc mutation
(add_parent/add_child/remove_parent/remove_child, which do maintain the
parents cache) is recorded as a separate follow-up.

Tests

Full suite green: 501 CT + 135 EUnit = 636, 0 failures, 0 compile warnings.
New: 2 EUnit (has_template_update/1) + 10 instance CT (remove ×5, update single
×4, _both ×1) + 3 mgr CT (mutate remove / update / mixed-rollback). Coverage
includes duplicate-edge ambiguity, /4 disambiguation, dangling-half-edge
rollback, direction independence, Template-AVP protection and survival, and
whole-batch atomic rollback. verify_caches/0 clean after every case.

Design: docs/designs/slice-e-relationship-mutation-design.md
Plan: docs/superpowers/plans/2026-06-28-slice-e-relationship-mutation.md

🤖 Generated with Claude Code

[david-w-t]

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