Symposium & Dial9: A plugin reference's declared version is accepted and ignored

[Fluzko]

Part of #294.

Depends on: nothing.

What happens

A chained plugin reference can declare a version: source.cargo = { name = "x", version = "=1.2.3" }. It is parsed, validated as a real version requirement, stored, and then never read. The resolver enqueues the reference without it, so the crate resolves as though no version had been given.

This is already known: md/rfds/registry-centric-plugins/README.md records it under future work as "chained-edge version enforcement", and describes the intended behaviour as comparing the resolved version against the recorded requirement and warning or skipping on mismatch. So this issue is a request to schedule that, plus one thing the future-work note does not cover.

plugin validate reports such a manifest green, with no warning. The tool actively tells the author they are fine about a field that does nothing. Whatever is decided about enforcement, accepting a field that is discarded is worth fixing on its own, and it is the part that bit a real crate author, because the crate-author documentation recommends this field for versioning skills separately from the library, which is exactly what it cannot do.

A note on how not to implement it

The RFD's direction (compare the already-resolved version) avoids a trap. If the requirement were instead pushed into the resolver, it would skip the fast path used for crates the workspace has already resolved and fall through to a registry lookup. A pinned reference to a crate developed locally and not published would then install nothing at all: zero skills, exit zero, no error, the failure recorded only in the log. That is a monorepo's own layout. It would also reach the network, which costs the per-event hook path its offline guarantee.

How to see it

# needs: cargo-agents, network, and an isolated SYMPOSIUM_HOME. Create the directories
# yourself; nothing below does.
#
# mkdir -p /tmp/iso /tmp/reg/d9
# /tmp/iso/config.toml: the [[registry]] entry is required. Without it `sync` never
# reads /tmp/reg and installs nothing, even though `plugin validate` below is happy:
#
#   [defaults]
#   symposium-recommendations = false
#   user-plugins = false
#
#   [[agent]]
#   name = "claude"
#
#   [[registry]]
#   name = "local"
#   path = "/tmp/reg"
#   auto-update = false
#
# /tmp/reg/d9/SYMPOSIUM.toml:
#
#   name = "d9"
#   depends-on = ["dial9-tokio-telemetry"]
#   [[plugins]]
#   source.cargo = { name = "dial9-viewer", version = "=0.3.13" }
#
# and a consumer project depending on dial9-tokio-telemetry

SYMPOSIUM_HOME=/tmp/iso cargo agents plugin validate /tmp/reg
# -> d9 (plugin)     green, with no warning that the version will be ignored

SYMPOSIUM_HOME=/tmp/iso cargo agents sync
ls .claude/skills | grep -c dial9
# -> 10, the newest set. 6 would mean the pin had been honoured:
#    dial9-viewer 0.3.13 ships 6 skills and 0.5.0 ships 10.

Done when

• A declared version is either enforced or rejected at validation time. Accepting a field that is then discarded is the defect, independently of which way it is resolved.
• If enforced: the resolved version is compared against the requirement, without losing the fast path for crates the workspace has already resolved, and without adding a network call to the per-event hook path. A test covers a locally developed, unpublished crate.
• The crate-author documentation stops recommending the field for something it cannot do, or starts being true. (Tracked in Symposium & Dial9: Documentation contradicts the code in eight statements #293.)