Ceylon 2.1 module metadata incompatible with Ceylon 3.0 runtime

Direct answer

No verified Ceylon 2.1 or Ceylon 3.0 releases exist in the model knowledge base. Publicly documented Ceylon language releases are in the 1.x series, e.g., 1.3.x. Because of that, the precise module-info fields that a Ceylon 3.0 runtime would reject from a Ceylon 2.1 compilation output cannot be confirmed, the behavior of a "ceylon workspace restore" command across a 2.1 to 3.0 major boundary cannot be confirmed, and there is no confirmed standard "shared" keyword in the Ceylon module system with a documented interaction model to Java JPMS.

Confirmed facts

• Model knowledge contains no verified release notes, module descriptor specification, or runtime behavior for Ceylon 2.1 or Ceylon 3.0.
• No verified description of a "ceylon workspace restore" command preserving module identifiers and versions across major version boundaries is available.
• No confirmed "shared" keyword in Ceylon module metadata and no documented Ceylon shared module to JPMS registration mapping is available.

Likely explanation if such versions existed

If a major toolchain bump from 2.x to 3.x were real, rejection would typically be driven by descriptor version and language version compatibility checks, not by individual application code. Major version bumps in language toolchains historically change module descriptor serialization and the language version tag accepted by the runtime. Workspace restore would normally require toolchain compatibility; preservation of identifiers and versions across an incompatible toolchain would be unexpected and would likely require explicit migration.

Class-path conflicts between versioned modules and JPMS-registered modules are a general risk when two module systems are mixed, but the specific manifestation for a Ceylon "shared" module cannot be confirmed without a verified specification.

Steps needed for this case

1. Verify the actual toolchain in use. Run ceylon --version on each development machine and CI agent and record the output.
2. Inspect a compiled module artifact. Locate the module descriptor file inside the compiled module and note the descriptor version and language version fields present.
3. Attempt a reproducible load in an isolated environment and capture the exact error output when loading the module with the runtime you have installed.

One missing diagnostic detail that changes the recommendation: the exact version string reported by ceylon --version and the contents of the module descriptor file from a failing module. With those, the claim of a 2.1 to 3.0 incompatibility can be tested against real artifacts instead of unverified version names.