Extension SDK: why does contentExclusion.checkPaths return available:false for a local Windows worktree?

[coolinker]

Question

GitHub’s [September 2 announcement](https://github.blog/changelog/2026-09-02-content-exclusions-generally-available-in-copilot-app-and-cli/) and [current support matrix](https://docs.github.com/en/copilot/concepts/context/content-exclusion#availability-of-content-exclusion) say Copilot App and CLI support content exclusions for Business and Enterprise customers.

How does that product-level support apply to extensions joined to an App session? Specifically, what is the supported way to obtain permission- and content-exclusion-checked access to local source files when session.rpc.contentExclusion.checkPaths returns available: false?

I am building source citations with a bounded hover preview. The production source-reading feature remains disabled rather than treating an unavailable policy check as permission to read.

Environment observed during investigation

• Windows

• Copilot App: 1.1.20

• Bundled Copilot CLI package: 1.0.84-5

Observed behavior

In an earlier synthetic probe, the joined-extension session/worktree identity checks passed and the native view tool was listed as available. A policy check for one newly created, harmless test file in that session’s own local worktree returned:

JSON

{"available":false,"checks":[]}

The call was equivalent to the following, where syntheticFilePath is the absolute path to that test file:

JavaScript

await session.rpc.contentExclusion.checkPaths({
  paths: [syntheticFilePath]
});

The probe stopped before invoking the native reader or reading the test file’s contents. This result does not identify a confirmed exclusion or user denial. I have not established the cause.

Help requested

1. Supported configuration: Is checkPaths supported for extensions joined to App sessions on Windows? What minimum App/CLI versions and session/authentication prerequisites apply?

2. Diagnosing unavailability: Is there a supported, redacted diagnostic that distinguishes policy-service readiness/binding, an unsupported session filesystem, and evaluation failure? The [documented limitations](https://docs.github.com/en/copilot/concepts/context/content-exclusion#limitations-of-content-exclusion) mention remote filesystems and symlinks. How can an extension determine whether its App-managed session filesystem is supported, even when the worktree is on local disk?

3. Intended read path: Should an extension use checkPaths before reading, or invoke the offered native view tool through session.rpc.tools.execute? Does that native invocation independently enforce both read permissions and content exclusions before returning file contents? What source path/range/version metadata can the extension rely on to bind a citation to the bytes actually read?

If this is a known limitation or fixed integration issue, a supported recovery procedure or version reference would help.

I am looking for the supported, fail-closed integration path, not a policy bypass or private runtime API. I can share further synthetic-probe details through an appropriate support channel; no private paths, source contents, credentials, or diagnostic bundles are included here.