[#4253 4/8] feat(holder): thread initialBindings through BuildSubmission

[stevenvegt]

Parent PRD

#4253

Item 4 of 8. Depends on item #3 (#4284) — branched off 4253-3-rewire-select, retargeted up the stack as dependencies merge.

Summary

Add an initialBindings map[string]string parameter to Wallet.BuildSubmission for the captured cross-VP bindings (Policy 2), kept distinct from the user's credentialSelection. Pure, behavior-neutral plumbing — every caller passes nil in this PR, so nothing changes until #5 wires the two-VP caller to pass the filtered captured bindings.

Why a separate parameter (not reuse credentialSelection)

• credentialSelection is the user's explicit selection, validated as user input at the API layer (Add verifiable data registry #6).
• initialBindings is the captured org-side binding from the two-VP flow, internal plumbing.

They must stay separate at the BuildSubmission boundary. Merging captured values into credentialSelection at the caller is exactly the applyCapturedFieldsToSelection behavior the PRD removes (PRD problem #1 / Policy 2). They travel separately and merge only inside the presenter when it builds Select's single bindings map. Per Policy 2 they cannot conflict (user values already filtered the org selection, so captured values agree); the merge gives the user credentialSelection precedence defensively.

Implementation Spec

Signature gains initialBindings map[string]string after credentialSelection, before params:

• vcr/holder/interface.go:56 — interface declaration.
• vcr/holder/sql_wallet.go:83 — implementation; thread the param to presenter.buildSubmission.
• vcr/holder/memory_wallet.go:63 — second implementation; same change.
• vcr/holder/presenter.go buildSubmission — add the param; merge credentialSelection + initialBindings (user precedence) and pass the merged map to builder.SetInitialBindings. With all callers passing nil, the merge is inert in this PR.
• vcr/holder/mock.go — regenerate via go generate ./vcr/holder/... (mockgen); update MockWallet.BuildSubmission and its recorder.

Callers pass nil for the new parameter:

• auth/api/iam/openid4vp.go:321 → BuildSubmission(ctx, []did.DID{walletDID}, nil, *presentationDefinition, nil, nil, buildParams).
• auth/client/iam/openid4vp.go:465 → add nil for initialBindings. (Moved Nuts-Network to Nuts-Node and implemented RFC004 #5 replaces this nil with the captured org bindings filtered to the SP PD's field ids.)

Testing

• Existing vcr/holder and auth/... tests pass after the signature change (call sites updated, mock regenerated). No new behavior to assert here — Moved Nuts-Network to Nuts-Node and implemented RFC004 #5 adds the behavioral test for captured bindings.
• A presenter-level unit test that a non-nil initialBindings is merged into the bindings handed to the match (so Moved Nuts-Network to Nuts-Node and implemented RFC004 #5 can rely on it) — minimal, can also live in Moved Nuts-Network to Nuts-Node and implemented RFC004 #5.

Acceptance Criteria

• BuildSubmission (interface + sql_wallet + memory_wallet) takes initialBindings map[string]string; mock regenerated.
• Presenter merges credentialSelection + initialBindings (user precedence) into the builder's initial bindings.
• Both callers updated to pass nil; no behavior change in this PR.
• go build ./... and go test ./vcr/holder/... ./auth/... pass.

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