This Week in Extensibility: six vendors standardize agent-plugin bundles, Mozilla stays neutral on WebMCP, Atlassian opens Rovo to Forge apps

2026-08-07T00:00:00-04:00

The theme this week was a split between packaging and trust. Six rival agent vendors agreed on how to bundle plugins while deliberately leaving security out of scope, Chrome began enforcing store rules that police what an extension may do, and the browser engines filed divergent positions on the API that would let a page hand tools to a user's agent. The packaging layer is converging faster than the trust layer underneath it.

Packaging: six vendors standardize agent-plugin bundles

Amazon, Cursor's maker Anysphere, GitHub, Microsoft, OpenAI, and Vercel published Agent Plugins 1.0.0, a vendor-neutral format for packaging agent extensions. The specification, announced August 6 in a joint post from Vercel, defines a bundle of a plugin.json manifest, a skills/ folder, and an mcp.json file so one plugin installs across ChatGPT, Codex, Cursor, GitHub Copilot, Kiro, and VS Code rather than being repackaged per client. It is labeled a Working Draft, and it carries no permission model, sandboxing, code signing, or secrets mechanism, with each of those deferred to future work; every client keeps its own trust and marketplace decisions.

Why it matters: the same customization, a set of Skills and MCP tools, becomes portable across the major agent clients instead of tied to one vendor's format, so a user is not re-installing per platform. The vendors standardized the bundle while leaving the permission and signing model to each client, so the portability is real and the safety guarantees are not yet part of the standard.

Standards: Mozilla files a neutral position on WebMCP

Mozilla recorded a neutral position on WebMCP, leaving the three browser engines split. WebMCP lets a website expose in-page tools that a user's own agent can call. Mozilla's August 5 position is neutral, while Apple's WebKit team has filed an oppose position citing privacy, security, venue, and API-design concerns, and Google and Microsoft are authoring the proposal. WebMCP remains a Web Machine Learning Community Group draft shipping only as a Chrome origin trial, so there is no cross-vendor agreement and no stable implementation.

Why it matters: the API that would let any site offer tools to a user's agent now has explicit, divergent positions from every engine, which points to a contested track rather than one converging toward shared support. It does not change that the only running implementation is a single browser's origin trial.

Marketplaces: Chrome Web Store begins enforcing its updated policies

Chrome Web Store policy enforcement began August 1 across its extension ecosystem. Four policies published July 1 took effect: a Limited Use rule narrowing data collection to what is strictly necessary for an extension's single disclosed purpose, a duty to notify users of post-install changes to data handling, a Regulated Goods ban on extensions enabling real-money prediction-market transactions, and a Malicious Products clause that bans extensions built to circumvent an AI service's safety guardrails or usage restrictions. Non-compliant extensions face enforcement after the date.

Why it matters: a marketplace of this reach setting a hard rule against extensions that defeat AI guardrails draws a governance line at the store level, where the platform, not each AI service, decides that circumvention tooling is not distributable.

Platforms: Atlassian opens Rovo to Forge apps and extends its Connect deadline

Atlassian shipped an Early Access Rovo MCP Module that lets Forge apps expose their actions as tools inside Rovo Studio. The August 3 changelog entry lets a Forge app publish its actions as callable tools for makers building custom agents in Rovo, extending the app platform into Atlassian's agent framework rather than shipping a single agent. In the same window Atlassian extended Connect end-of-support to January 31, 2027, moving the deadline out of the year-end crunch, and began direct outreach to vendors still running Connect or hybrid apps so they migrate to Forge.

Why it matters: it gives Marketplace developers a supported path to surface their apps as tools inside Atlassian's agents, while the Connect deadline sets the date by which the whole ecosystem must be on Forge to reach that surface at all.

Also worth knowing

Merge added a governed catalog of MCP connectors to its Agent Handler. A July 31 changelog lets a company embedding Merge browse and enable hundreds of generic MCP connectors alongside Merge-built ones on the same authentication, access-control, and governance layer, and adds an AI Guardrails experience with PII detection and a live rule tester.

Wasmtime patched two sandbox-integrity advisories across four release lines. The Bytecode Alliance shipped v47.0.3 and matching v46, v36, and v24 releases on July 31 to fix two low-severity advisories where engine type indices could be confused and where traps during bulk operations could corrupt VM state. Backporting to the v24 long-term line reflects Wasmtime's use as production plugin-isolation infrastructure.

CopilotKit released a Channels SDK for running AG-UI agents in chat surfaces. The August 4 SDK runs one AG-UI agent across Slack, Teams, and other chat platforms with generative UI, human-in-the-loop approvals, and cross-channel memory. It is a developer library for shipping agents rather than a customization surface handed to end users.

On the radar

August 13–14: MCP Dev Summit in Seoul, co-located with Open Source Summit Korea.
September 1: Atlassian Forge Object Store currentVersion field deprecation takes effect.
September 30: Atlassian sunsets the confluence:fullPage and jira:fullPage modules in favor of a unified global:fullPage.
January 31, 2027: Atlassian Connect end-of-support; Marketplace and custom apps must be on Forge.

This Week in Extensibility is curated by Todd Schiller. Research, drafting, and fact checking are AI-assisted.