feat(cache): cache model schemas in the daemon

[GareArc]

Description

Follow-up to #780. Same ownership problem, different cache — not required to fix #3547, so it ships separately.

Dify caches model schemas under a key built from the plugin id with no version:

# api/core/plugin/impl/model_runtime.py
cache_key = f"{self.tenant_id}:{provider}:{model_type.value}:{model}:{cache_user_id}"

provider resolves to the plugin id, so an upgrade does not change the key. Nothing invalidates it either — the only redis_client.delete on that path fires when a cached blob fails to parse as AIModelEntity, which catches a shape change but not a value change. An enterprise-side plugin upgrade therefore serves stale schemas for up to PLUGIN_MODEL_SCHEMA_CACHE_TTL (1h by default), and Dify has no way to learn about it.

What changed

Cache them here instead, keyed on PluginUniqueIdentifier, which pins version and checksum. An upgrade lands on a different key, so a stale entry is unreachable and nothing needs to invalidate this cache — the same content-addressed trick CombinedGetPluginDeclaration already uses. Credentials are folded in as a digest, as Dify does today.

GetAIModelSchema moves out of the generated dispatchers, following the InvokeAgentStrategy precedent already commented into definitions.go. The generated service body calls baseSSEWithSession, which creates a session before the callback runs; a cache hit that still creates a session and dispatches to the plugin would not be saving anything. The hand-written service answers a hit directly in the same SSE wire format.

On a miss the response stream is teed via Filter + OnClose, storing only if exactly one chunk arrived with a non-nil schema, so an error mid-stream caches nothing.

Remote and debugging plugins keep one identifier across code changes and are never cached — otherwise a developer iterating on a plugin would be served their own stale build.

TTL defaults to 60 minutes via PLUGIN_MODEL_SCHEMA_CACHE_TTL; since the key is content-addressed it only bounds memory.

Separate first commit

The generator still wrote to internal/core/plugin_daemon, which was renamed to io_tunnel, so go run cmd/codegen/main.go failed partway and left the tree half-regenerated. Regenerating with the corrected path also settles import ordering in files that had been reformatted by hand after the last run.

Type of Change

• Bug fix
• New feature
• Refactor
• Performance improvement
• Other

Essential Checklist

Testing

• I have tested the changes locally and confirmed they work as expected
• I have added unit tests where necessary and they pass successfully

4 tests in pkg/utils/cache/helper cover the round trip, keyed-on-version, keyed-on-credentials, and the remote-plugin skip. go build, go vet and gofmt are clean, and /model/schema is verified to register exactly once per router group.

Not verified locally: the endpoint end-to-end, which needs a running daemon with an installed plugin. The SSE cache-hit path is the piece most worth exercising against a real request before this leaves draft.

Additional Information

Only useful once PLUGIN_MODEL_SCHEMA_CACHE_ENABLED (langgenius/dify#39632) is turned off; until then Dify never calls through on a hit of its own cache.

Independent of #780 — the two touch the same four config files but no shared logic, so they can merge in either order.