Compaction must preserve verifiability

[Fury03]

Backlog entry #133, from docs/backlog.md — Initiative D — V3 Foundations / D4 — Storage and scale.

What

Any scheme that drops records must keep the chain checkable, or the property the package exists for is lost.

Dependencies

Blocked on #201 (backlog #131). Do not start until that lands — the data or contract this depends on does not exist yet.

Roadmap impact

V3 — Market structure & history — D4 — Storage and scale.

Constraints that apply

From CONTRIBUTING.md — hard constraints, not style preferences:

• decimal.Decimal for all money; no float64 in any pricing path
• an unavailable quantity is unknown, never zero and never a default
• checks and metrics qualify the headline; they never move a verdict or an
  integrity state
• nothing is ever synthesised to fill a gap — if a figure cannot be obtained,
  the correct output is an error or an explicit unknown

Done when

• the behaviour described above is in place in the file(s) named
• tests cover it, running offline from recorded fixtures wherever upstream
  data is involved
• make fmt vet test race lint passes
• anything user-visible is reflected in the README or docs/

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Scope and acceptance criteria may be sharpened in the comments before work starts — say so in a comment if you are picking this up. If the work turns out to require changing verdict thresholds, integrity semantics, the check composition rule or the run-record layout, stop and flag it: that is a different issue with a different review bar.