docs(internet-identity): use mo:identity-attributes for the Motoko attribute flow

[sea-snake]

Summary

Updates the internet-identity skill's identity-attributes guidance to use the mo:identity-attributes mixin on the Motoko side, and reframes the frontend + Rust backend around the library's two-method protocol (_internet_identity_sign_in_start / _internet_identity_sign_in_finish) so a single frontend works against either backend.

Changes

• Prerequisites / compatibility: mo:identity-attributes >= 0.4.0 (pulls mo:core >= 2.5.0; needs moc >= 1.6.0 for include).
• Frontend (AuthClient): nonce, sign-in, and requestAttributes run in parallel (nonce passed as a promise); requests name + verified_email; checks the { ok }/{ err } result from _internet_identity_sign_in_finish.
• Motoko backend: include IdentityAttributes({ onVerified }) replaces the hand-rolled ICRC-3 decode + lookup helpers.
• Rust backend: implements the same two methods by hand (manual ICRC-3 decode, explicit signer/origin/nonce/freshness checks), explicitly mirroring what the library does internally — there is no Rust library yet.
• Env vars: the Motoko path now documents frontend_origins (+ optional trusted_sso_domains) alongside trusted_attribute_signers.
• Pitfalls Fix round 7: canister_self, StableCell<Principal>, evm-rpc import path #9/Rewrite https-outcalls Rust for ic-cdk 0.18 API #10 updated to reference the library and the protocol method names.
• Evals: updated the admin-allowlist case (Motoko now via the mixin) and added a new case for the Motoko mixin pattern.

Verification

• node scripts/check-project.js passes (metadata + eval schema).
• The repo's skill-validator check could not run in the sandbox: the npm name skill-validator resolves to an unrelated package with no check subcommand. CI runs the real agent-ecosystem/skill-validator. Code-fence balance and frontmatter were verified manually.
• Output-eval suite not re-run (recommended-not-required for improvements; needs the claude CLI per case).

[github-actions]

Skill Validation Report

Validating skill: /home/runner/work/icskills/icskills/skills/internet-identity

Structure

• Pass: SKILL.md found

Frontmatter

• Pass: name: "internet-identity" (valid)
• Pass: description: (325 chars)
• Pass: license: "Apache-2.0"
• Pass: compatibility: (45 chars)
• Pass: metadata: (2 entries)

Tokens

• Warning: SKILL.md body is 6666 tokens (spec recommends < 5000)

Markdown

• Pass: no unclosed code fences found

Tokens

File	Tokens
SKILL.md body	6,666
Total	6,666

Content Analysis

Metric	Value
Word count	3,537
Code block ratio	0.35
Imperative ratio	0.07
Information density	0.21
Instruction specificity	0.94
Sections	14
List items	37
Code blocks	8

Contamination Analysis

Metric	Value
Contamination level	low
Contamination score	0.14
Primary language category	config
Scope breadth	3

• Warning: Language mismatch: javascript, systems (2 categories differ from primary)

Result: 1 warning

Project Checks

✓ Project checks passed for 1 skills (0 warnings)