docs: add ERC-8004 interop documentation

[kawacukennedy]

This PR adds documentation for the ERC-8004 (Kuberna Labs) interop with AIP, as discussed in issue #1.

Changes:

1. docs/competitive-analysis.md: New section for ERC-8004 with status, strengths, limitations, and AIP relationship describing how the two protocols complement each other (off-chain fast path via AIP, on-chain durable record via ERC-8004). Also adds ERC-8004 entry to the Other Emerging Projects comparison table.

2. spec/aip-core.md: Adds erc8004 extension field example to the identity document JSON schema, updates the extensions field description, and adds ERC-8004 to the design decisions note.

Interop pattern: An AIP identity document can include an erc8004 extension linking to an agent's on-chain registration, while an ERC-8004 delegation can reference an AIP token's scope as off-chain context. The adapter library consuming AIP as a primitive will live in the Kuberna Labs repos (separate PR).

Summary by CodeRabbit

Documentation

• Added a new ERC-8004 (Kuberna Labs) section to the competitive analysis, including status, on-chain strengths/limitations, and a reference link.
• Updated comparison table of emerging projects to include ERC-8004 and its bridging considerations.
• Updated the AIP spec to explicitly support ERC-8004, including example identity extension fields and normative extension rules.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: d3dc397c-d90e-4576-bd75-d69d30c6d15a

📥 Commits

Reviewing files that changed from the base of the PR and between a996e2e and 9ea8964.

📒 Files selected for processing (2)

• docs/competitive-analysis.md
• spec/aip-core.md

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📝 Walkthrough

Walkthrough

This PR integrates ERC-8004 (Kuberna Labs) protocol support into the AIP documentation. It adds competitive analysis describing ERC-8004 as a complementary emerging project and updates the AIP core specification to recognize ERC-8004 as an officially supported extension.

Changes

ERC-8004 Support Documentation

Layer / File(s)	Summary
Competitive analysis documentation docs/competitive-analysis.md	New "ERC-8004 (Kuberna Labs)" subsection describes the protocol's development status, strengths, limitations, and complementary relationship to AIP (off-chain token fast path vs on-chain durable registry/settlement). Table entry added to "Other Emerging Projects" comparison and a reference link was added.
AIP core specification updates spec/aip-core.md	Identity document example adds an erc8004 entry under extensions; new extensions.erc8004 subsection provides a normative JSON schema, validation rules, and semantics for linking identity documents to on-chain ERC-8004 agent identities. The extensions field definition and Design Decisions now list ERC-8004 alongside LDP and OAuth.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐰 I found a new ledger in the night,
ERC-8004 glows soft and bright,
I nibble docs and hop with glee,
Two paths — on-chain and AIP — for me! 🥕✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding documentation for ERC-8004 interoperability between AIP and Kuberna Labs.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@docs/competitive-analysis.md`:
- Around line 128-143: Add a primary source link for ERC-8004 by inserting the
official EIP/spec/repo URL into the ## References section and then cite it
inline next to the "Status: Draft EIP, active development." line and the later
"ERC-8004" mention; specifically, update the text that includes "Status: Draft
EIP, active development." and the paragraph referencing "ERC-8004" to include a
parenthetical or bracketed citation pointing to the new References entry so the
deployment/status and claims are verifiable.

In `@spec/aip-core.md`:
- Around line 120-122: Add a small normative subsection that defines
extensions.erc8004: require an object with required keys "chain_id" (positive
integer) and "address" (string containing a 20-byte hex Ethereum-style address,
prefixed with 0x and validated as hex; optionally state checksum/case rules),
and allow an optional "metadata" object for freeform fields; specify types,
example JSON, and a short validation rule (e.g., JSON Schema fragment or
explicit bullet rules) and apply this definition wherever extensions.erc8004 is
referenced (the three occurrences) so producers/consumers can interoperate using
the functions/constructs named extensions.erc8004, chain_id, and address.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 9a4dcd6c-2b9f-4c9e-9058-b9d838214f9a

📥 Commits

Reviewing files that changed from the base of the PR and between b3dc854 and a996e2e.

📒 Files selected for processing (2)

• docs/competitive-analysis.md
• spec/aip-core.md

[kawacukennedy]

Addressed both CodeRabbit review comments in commit 9ea8964:

1. ERC-8004 citation — Added [ERC-8004] reference link to the References section pointing to the EIP draft, and cited it inline at both the status line ("Status: Draft EIP, active development [ERC-8004]") and the relationship paragraph.

2. Normative extensions.erc8004 schema — Added Section 3.2.1 defining:

   • chain_id (REQUIRED, positive integer, EIP-155 chain ID)
   • address (REQUIRED, 20-byte hex with 0x prefix, checksum optional)
   • metadata (OPTIONAL, freeform object)
   • Validation rules, forward compatibility, and extension semantics
   • JSON example matching the existing identity document in Section 3.1