Add client-side bidder support for Prebid.js

[ChristianPavilonis]

Summary

• Allow specific Prebid.js bidders to run client-side in the browser instead of routing all bidders through the server-side auction. Some adapters (e.g. Magnite/Rubicon) do not work well with Prebid Server.
• Adds a new client_side_bidders config field — bidders in this list stay as standalone native Prebid.js bids and are not absorbed into the trustedServer adapter.
• Adds a build-time adapter selection system (TSJS_PREBID_ADAPTERS env var) so operators can control which native Prebid.js adapters are bundled without code changes.
• Backward compatible: an empty list preserves current behavior (all bidders go server-side).

Auction flow

flowchart TD
    A["Publisher Page<br/>pbjs.requestBids()"] --> B["requestBids Shim<br/>(tsjs-prebid)"]
    B --> C{"Is bidder in<br/>clientSideBidders?"}
    C -- "Yes (e.g. rubicon)" --> D["Leave as standalone bid<br/>Native Prebid.js adapter"]
    C -- "No (e.g. kargo, appnexus)" --> E["Absorb into trustedServer<br/>bidderParams"]
    E --> F["POST /auction<br/>Trusted Server Orchestrator"]
    F --> G["Prebid Server (PBS)<br/>OpenRTB 2.x auction"]
    G --> H["Server-side bids returned<br/>(kargo, appnexus, etc.)"]
    D --> I["Client-side bid<br/>(rubicon via rubiconBidAdapter.js)"]
    H --> J["Prebid.js auction<br/>All bids compete"]
    I --> J
    J --> K["Winning bid rendered"]

    style C fill:#f9f,stroke:#333
    style D fill:#bfb,stroke:#333
    style E fill:#bbf,stroke:#333

Loading

Configuration example

[integrations.prebid]
bidders = ["kargo", "appnexus", "openx"]         # server-side via PBS
client_side_bidders = ["rubicon"]                  # native browser adapters

Changes

File	Change
crates/common/src/integrations/prebid.rs	Added client_side_bidders: Vec<String> to PrebidIntegrationConfig with #[serde(default, deserialize_with)]; added field to InjectedPrebidClientConfig with skip_serializing_if; added duplicate-bidder warning when a bidder appears in both lists; updated base_config() test helper; added 2 tests for head injector serialization
crates/js/lib/src/integrations/prebid/index.ts	Imports generated adapter barrel file (_adapters.generated.ts) and adapterManager; added clientSideBidders to InjectedPrebidConfig interface; reads config into a Set; skips client-side bidders when building bidderParams for trustedServer; validates that each client-side bidder has a registered adapter at init
crates/js/lib/src/integrations/prebid/_adapters.generated.ts	New generated file — barrel of import statements for each adapter listed in TSJS_PREBID_ADAPTERS (defaults to rubicon)
crates/js/lib/build-all.mjs	Added generatePrebidAdapters() that reads TSJS_PREBID_ADAPTERS env var, validates adapter modules exist in prebid.js/modules/, and writes _adapters.generated.ts; added Vite resolve.alias for prebid.js/src/adapterManager.js
crates/js/lib/vitest.config.ts	Added resolve.alias for prebid.js/src/adapterManager.js so tests can resolve the module
crates/js/lib/test/integrations/prebid/index.test.ts	Added mocks for _adapters.generated.ts and adapterManager; added 8 new tests covering client-side bidder edge cases
crates/js/lib/package-lock.json	Dependency updates from prebid.js module resolution
trusted-server.toml	Moved rubicon from bidders to new client_side_bidders; added documentation comment

Closes

Closes #471
Closes #463

Known limitations

• Adding a new client-side bidder requires setting TSJS_PREBID_ADAPTERS at build time (e.g. TSJS_PREBID_ADAPTERS=rubicon,appnexus) and rebuilding the JS bundle — no code changes needed.
• The bidders and client_side_bidders lists are independent — the operator manages both explicitly. A warning is logged at startup if a bidder appears in both.

Test plan

• cargo test --workspace
• cargo clippy --all-targets --all-features -- -D warnings
• cargo fmt --all -- --check
• JS tests: cd crates/js/lib && npx vitest run
• JS format: cd crates/js/lib && npm run format
• Docs format: cd docs && npm run format — pre-existing: prettier not installed in docs/
• WASM build: cargo build --bin trusted-server-fastly --release --target wasm32-wasip1
• Manual testing via fastly compute serve

Checklist

• Changes follow CLAUDE.md conventions
• No unwrap() in production code — use expect("should ...")
• Uses tracing macros (not println!)
• New code has tests
• No secrets or credentials committed

[prk-Jr]

👍 Looks good