ISA

The ISA is the single document that articulates "done" for any thing whose ideal state we are pursuing — a project, an application, a library, infrastructure, a work session, an art piece, a strategic decision. It serves five identities at once: ideal state articulation, test harness, build verification, done condition, system of record. This skill owns the canonical template, the workflows that generate and refine ISAs, and the example library.

Most work starts without a written, testable definition of what finished looks like, so "done" drifts — the goal in your head at the start isn't the goal you settle for at the end, and there's no record of which one was right. Criteria stay vague enough that anything passes, decisions and dead ends get forgotten and re-litigated, and when work spans multiple sessions or multiple agents there's no shared source of truth for what's been verified. The ISA fixes "done" as a hard-to-vary explanation with atomic, probe-able criteria, a stable-ID structure that survives edits, and an audit trail of what was conjectured, refuted, and learned.

The ISA is a single document with a locked twelve-section body. A tier completeness gate decides which sections are required at which effort level, and five workflows generate, deepen, score, and reconcile the artifact across sessions and agents.

Every ISA may have up to twelve body sections. The tier completeness gate decides which are required at which effort tier; sections never appear empty. Order is fixed.

Adjacent concepts. Distinguished by who they bind.

The first three are author-stated (declarative). Anti-criteria are derived — they are how Out of Scope, Constraints, and Principles become probe-able.

Mirrors the v6.1.0 thinking-floor non-relaxability. Required sections per tier:

Project ISA override: any <project>/ISA.md requires E3+ structure regardless of the active task's tier. The project file is the long-lived source of truth; one transient E1 task must not downgrade it.

CheckCompleteness workflow enforces this gate. A miss blocks phase: complete until the missing sections are filled in.

The highest-information-density part of this skill. Each entry captures a non-obvious failure mode that has bitten real ISA work.

• ID-stability is the cornerstone of Reconcile — never re-number on edit. When the Splitting Test produces a finer-grained version of ISC-7, preserve ISC-7 as the parent and add ISC-7.1, ISC-7.2, etc. Even when an ISC is dropped, leave a tombstone (- [ ] ISC-N: [DROPPED — see Decisions YYYY-MM-DD]). Reconcile keys on stable IDs; renumbering breaks ephemeral feature-file merges silently and the failure mode looks like "the worker's checkmarks didn't land in master."
• Ephemeral files are derived views, never sources of truth. Scaffold's --ephemeral mode produces a slice of the master ISA at MEMORY/WORK/{slug}/_ephemeral/<feature>.md. Workers operate against that slice; Reconcile merges back. Hand-editing master content from an ephemeral file is policy-forbidden — the master is what persists; the ephemeral is what gets archived.
• The Changelog format is non-negotiable. Every entry needs all four pieces (conjectured, refuted by, learned, criterion now) in that order. Append refuses to write a partial C/R/L; if any of the four is missing, the entry is a Decision, not a Changelog. The format is what makes the Deutsch error-correction trail auditable across sessions.
• Project ISAs upgrade tier to max(declared, E3) regardless of the active task's tier. A <project>/ISA.md is the long-lived system of record for a thing with persistent identity. One transient E1 task on the project must NOT downgrade the structural minimum. CheckCompleteness applies this override automatically.
• Empty sections never appear. The twelve-section body is a capacity, not a requirement at every tier. Sections required-but-empty for the tier are populated; sections not required and not yet written are simply absent from the file. CheckCompleteness distinguishes present / thin / missing / empty and only empty is acceptable for Verification before VERIFY phase.
• Anti-criteria are derived from Out of Scope plus regression-prevention concerns. They are how the prose-guardrails (Out of Scope, Constraints, Principles) become probe-able. At least one is required at every tier; the absence of an anti-criterion at OBSERVE is a hard CheckCompleteness failure.
• Antecedents are required when the goal is experiential. For art, design, content, and anything that has to "land," at least one ISC must use the Antecedent: prefix to name a precondition that reliably produces the target experience. Verifiable goals (build, deploy, schema) don't need antecedents; experiential goals always do.
• Reconcile is deterministic — there are no conflicts to resolve. Either an ISC ID exists in master (mechanical merge) or it doesn't (abort with ID-stability violation). If the ephemeral made structural changes (split ISC-7 into ISC-7.1/ISC-7.2), those structural changes belong in master via a separate Edit by the user before Reconcile runs.
• The format spec wins on contradiction. IsaFormat.md is the file-shape contract. If this skill's prose ever drifts from the format spec, the spec is canonical and the skill updates to match — not the reverse.

The Examples/ directory holds twelve reference ISAs spanning the tier (E1–E5) × domain (code / art / design / ops / marketplace / enterprise) matrix. Always start by reading the canonical showpiece before scaffolding a new ISA — copy its section headers, then populate. Pick the example closest to your domain + scale as a template.

Showpiece

Code

Art (experiential — antecedents required)

Design (experiential)

Ops

Enterprise

ISC IDs never re-number on edit. When the Splitting Test produces a finer-grained version of ISC-7, the original number is preserved as the parent and children become ISC-7.1, ISC-7.2, etc. Do not collapse the numbering even if the ISC is dropped — leave a tombstone marker so historical references in Decisions, Changelog, and Verification remain valid.

This rule exists because Reconcile is keyed on ISC IDs. If IDs renumber across edits, ephemeral feature-file reconciliation breaks silently. The renumbering ban is what makes feature-file workflows safe.

When a feature is to be worked in an isolated context (Ralph Loop, Maestro, parallel coding-agent instances), the Algorithm invokes:

Skill("ISA", "extract feature <name> as ephemeral file")

Scaffold (with --ephemeral mode) produces a derived view at MEMORY/WORK/{slug}/_ephemeral/<feature>.md containing only the slice relevant to that feature: the Vision and Goal as read-only context, the relevant Constraints, the ISCs in the feature's satisfies: list with stable IDs, the matching Test Strategy entries, and an empty Verification section.

A fresh-context agent operates against the ephemeral file alone. At completion, Reconcile deterministically merges ISC checkmarks, Verification evidence, Decisions entries, and any new Changelog entries back to master, then archives the ephemeral file under _ephemeral/.archive/.

Ephemeral files are derived views. They are never sources of truth. They are never hand-edited as policy. The master ISA is what persists.

The Algorithm at OBSERVE invokes this skill to scaffold or read an ISA. The skill does not run the Algorithm — it owns the artifact the Algorithm operates on.

• OBSERVE: Skill("ISA", "scaffold from prompt at tier T") → returns populated ISA at canonical location.
• OBSERVE: Skill("ISA", "check completeness of <path> at tier T") → pass/fail + gap report.
• PLAN: Skill("ISA", "extract feature <name> as ephemeral file") → ephemeral excerpt.
• LEARN: Skill("ISA", "reconcile <ephemeral-path> → <master-path>") → deterministic merge.

The Algorithm doctrine spec at ~/.claude/PAI/ALGORITHM/v6.2.0.md (or LATEST) governs invocation cadence. This skill is invocation-agnostic — it works the same whether called by the Algorithm or directly by the user.

The full ISA format spec lives at ~/.claude/PAI/DOCUMENTATION/ISA/IsaFormat.md. This skill implements that spec; if there is ever a contradiction, the format spec wins and this skill is updated to match.

The system-architecture doc — five identities, three-guardrail taxonomy, twelve-section body, six workflows, two homes, subsystem relationships — lives at ~/.claude/PAI/DOCUMENTATION/ISA/IsaSystem.md. Read that for the conceptual frame; read this file (and IsaFormat.md) for the operational contract.