Make `ResolveModelContentLength` honor the per-model custom **context window length** (`content_length`) — stored in the Python-legacy `tenant_model.extra["max_tokens"]` field, whose semantic meaning is the context window, NOT the generation cap — **before** any provider-catalog read, and remove the parallel service-layer implementation so every consumer shares one resolution path.
Switch the agent LLM component's `fitMessages` from the local map-based `messageFitInRaw`/`countAllTokens`/`stringContent`/`setContent` helpers to the new shared `internal/component/messagefit` package (#18091).
Replaces the Python agent canvas runtime with a Go implementation that
runs inside `cmd/server_main`.
The canvas compiles into an eino Workflow that pauses on wait-for-user
via native Interrupt/Resume (no sentinel flag) and resumes from a
Redis-backed CheckPointStore.
All 21 Python agent components and ~35 tools are ported with functional
parity.
Sandbox providers now read their JSON config from the admin-panel
system_settings table with env fallback.
234 files / +35,413 / -6,111. All Go files are gofmt-clean (CI gate
added); drops the v2 DSL E2E step and the gap-analysis plan (both
redundant after the port ships).
## Type of change
- [x] Refactoring
- [x] New feature
- [x] Bug fix
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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Co-authored-by: Claude <noreply@anthropic.com>
