Public-ready repository skill

Cost and ownership analysis

Maps scoped functions to algorithmic cost, input boundaries, and mutation ownership. Applies when a review raises complexity, helper reuse, repeated preparation, parsing, regex or prototype-chain behavior, path handling, or state-aliasing concerns that should change an implementation decision.

What this produces

A scoped function inventory with interpreted bounds or explicit compositional costs, ownership and exposure findings, fitting repairs and acceptance evidence when authorized, and one clear receiving decision.

Source and version

Repository path
.agents/skills/cost-and-ownership-analysis/SKILL.md
Source revision
cfaa53f5b7500e3901d8470e1e471cd0230ff2a5
Source SHA-256
3f7ec3bbaa7902d3939a9a2cdf2e9c6b14c1dc1b51bd4aea36faac785ce331b9
Publication standing
Public ready

Included source files

Complete skill source

The Markdown below matches the exact source text. The format link above opens the file on its own.

---
name: cost-and-ownership-analysis
description: Maps scoped functions to algorithmic cost, input boundaries, and mutation ownership. Applies when a review raises complexity, helper reuse, repeated preparation, parsing, regex or prototype-chain behavior, path handling, or state-aliasing concerns that should change an implementation decision.
---

# Cost and ownership analysis

## Contract

- **What:** A source-grounded account of scoped function cost, input boundaries, and mutation ownership, followed by the smallest authorized repair and its decision-changing evidence.
- **When:** Complexity or resource use may change a design, a security-shaped concern needs a precise mechanism, or state crosses validation, computation, rendering, exchange, and filesystem boundaries. Ordinary edits use the smallest relevant call path; a complete function inventory follows the requested scope.
- **Boundaries:** Current intent selects observation or implementation, revision, and receiving surface. Shared generated copies point to their canonical owner. External library, engine, DOM, and I/O costs retain explicit terms until evidence resolves them. Source-derived mechanisms, observed exploitation, measured performance, and release approval each retain their own evidence and authority.
- **Result:** A scoped function inventory with interpreted bounds or explicit compositional costs, ownership and exposure findings, fitting repairs and acceptance evidence when authorized, and one clear receiving decision.

## Rules

### Rule: Coverage has a coordinate

Bind the inventory to the requested revision and pending changes. Identify callable definitions, callback multipliers, recursion, generated code, and excluded dependencies. Distinguish complete enumeration from complete closed-form cost resolution.
### Rule: Reuse starts from the existing semantic owner

Before implementation, identify the owner and helpers that predate the current change wave, then compare their contract with the receiving task. Reuse fitting behavior at the smallest compatible boundary while preserving independent expectations, invocation-local state, and the receiving owner's lifecycle and evidence obligations.

### Rule: Cost follows the whole receiving path

State the variables, caps, expected lookup assumptions, worst-case or amortized model, and output size. Include repeated admission, key sorting, copying, serialization, projection, and derived-view preparation. Keep allocation volume distinct from peak live memory and garbage-collection pauses.
### Rule: Construction and compilation carry separate claims

Source can establish repeated object or schema construction. Engine cache reuse, native compilation, tiering, and wall-clock impact require fitting observations. Finite source-owned patterns can be prepared once; their grammar and input budget still carry the matching boundary.
### Rule: Loop cost follows total work

Name each independent input dimension and the progress measure of each loop. Nested syntax with one monotone cursor can have linear total work; repeated prefix scans, copies, descendant walks, or growing-list membership checks can introduce additional factors. Account for library parsing and browser layout separately. Emitted labels, serialized records, and other output expansion carry their own size term. A source-derived bound and a measured growth curve answer different questions.
### Rule: Security findings name their actual mechanism

Separate prototype-chain lookup from prototype mutation, regex source injection from expensive matching, and lexical path containment from physical filesystem identity. Name the input's actor, size, ownership, reachability, and execution context before assigning consequence.
### Rule: Pure boundaries clarify ownership

Prefer owned return values and explicit path-copy transitions. Keep invocation-local counters, indexes, and collectors when they preserve linear work. Detached results own their nested mutable values; immutable shared projections declare their reading contract. Rendering derives from accepted business state, while UI retention and I/O remain named adapters.
### Rule: Owned snapshots follow a bounded projection

Admit the canonical fields, collection lengths, variable-size values, and any declared extension envelope before copying. Retain those fields in owned mutable containers while leaving unrelated metadata outside the projection. A bounded core followed by a whole-input deep clone can still traverse unbounded surplus state; detachment and admission therefore retain separate checks.

### Rule: Preparation earns one authority

Keep public admission gates and compose trusted private calculation from admitted values. Cache by a complete semantic identity or immutable revision, preserve caller-owned inputs, and invalidate every dependent view when that identity changes.
### Rule: Evidence matches the claim

Use focused schema/runtime parity, state-immutability, round-trip, retained-UI-state, and path-boundary cases. Run adversarial matching in an isolated worker with an explicit timeout and cleanup. A timeout-bounded completion check establishes that budget; growth-rate or responsiveness claims require measured workloads and an appropriate environment.
### Rule: Return changes the next decision

Lead with actionable findings and their smallest repairs, retain valid boundaries, and name remaining uncertainty. Completion supplies the requested inventory, authorized changes, normalized evidence, and one receiving route. A new generic harness earns adoption through recurring turn savings or protection of a consequential boundary.

## Composition and receiving use

[Practitioner probe](../practitioner-probe/SKILL.md) supplies a focused mechanism question when the concern is ambiguous. [Stateful artifact behavior contracts](../stateful-artifact-behavior-contracts/SKILL.md) supplies behavior-specific acceptance. Desired-state, evidence-calibrated language shapes the handback, and [collaboration accounting](../collaboration-accounting/SKILL.md) carries decision-changing transfer evidence.

For engine claims, consult the runtime owner's current documentation. [V8 regex tier-up](https://v8.dev/blog/regexp-tier-up) explains why construction and native compilation differ. [OWASP prototype-pollution guidance](https://cheatsheetseries.owasp.org/cheatsheets/Prototype_Pollution_Prevention_Cheat_Sheet.html) supplies dictionary-boundary techniques; current source determines the specific mechanism and exposure.

Load [Python boundaries and traversal cost](references/python-boundaries-and-traversal-cost.md) when Python representation, source editing, package boundaries, or generated tests change the analysis. Other runtimes retain their own representation and enforcement rules.

Load [Ownership-preserving reuse](references/ownership-preserving-reuse.md) when choosing, extracting, or replacing a helper, parser, fixture, or preparation path. It supplies bounded owner discovery, contract comparison, and dependent-evidence invalidation.