test(cli): end-to-end coverage for witness exchange (export → sign → submit)

[mmlado]

Description

Closes #263

The witness exchange flow from #246 merged with unit coverage of the blob format but nothing exercised the commands themselves, and the submit path had only been compile-checked since the LEZ v0.2.4 WalletCore migration. This PR adds end-to-end coverage of the full export, sign, submit round trip against a live sequencer, plus deterministic failure-path tests for spel sign and spel submit.

The e2e run creates two wallets from scratch. Wallet A exports a partial transaction with --export and --co-signer, wallet B signs it with spel sign and submits it with spel submit, and the script asserts the transaction confirms in a block. Two failing paths are asserted along the way: submitting while a witness is still missing, and submitting a blob whose message was tampered with after signing. The tamper step flips one bit in the last byte of message_hex, which keeps the blob decodable so the rejection is specifically the signature check.

Verified locally against a freshly built LEZ v0.2.4 stack, all steps pass. That run is also the first live execution of the submit path since the v0.2.4 migration, which covers point 3 of the ticket.

Changes

• New scripts/multisig-e2e-test.sh, modeled on the existing e2e scripts. Starts its own sequencer on port 3044 and only ever kills a leftover process matching that port, never a running stack.
• New spel-cli/tests/exchange_flow.rs with four binary-level tests for sign_command and submit_command failure paths. All four reject before the wallet is touched, so they need no wallet home or sequencer.
• New CI job multisig-e2e-test, modeled on the init E2E job with the LEZ tag pinned to the revision from spel-framework/Cargo.toml.
• Dropped an unused import from spel-cli/src/exchange.rs.

Checklist

• Builds cleanly (cargo build -p spel)
• Tests pass (cargo test -p spel, 113 tests, plus the e2e script against LEZ v0.2.4)
• README updated if new features, CLI commands, or behaviour changed (tests only, no behaviour change)
• New public methods have doc comments (none added)
• Branch is off main (not another feature branch)

[Copilot]

🟢 Approval recommended

The changes are test/CI-focused, consistent with existing patterns in the repo, and the new coverage directly addresses the stated gaps without introducing behavioral changes.

Pull request overview

Adds comprehensive CLI-level coverage for the multisig witness exchange workflow, ensuring the export → sign → submit round trip is exercised end-to-end against a live LEZ sequencer and that key failure paths are tested deterministically at the binary level.

Changes:

• Adds a new E2E bash script that scaffolds a project, starts a dedicated sequencer, creates two isolated wallets, and validates the full witness-exchange round trip plus key rejection cases.
• Adds new Rust integration tests that execute the real spel binary to assert sign/submit reject unreadable blobs, missing witnesses, and tampered messages before wallet initialization.
• Extends CI with a dedicated “Multisig E2E” job wired to the shared LEZ build/caching setup.

File summaries

File	Description
spel-cli/tests/exchange_flow.rs	New binary-level integration tests for deterministic spel sign / spel submit failure paths.
spel-cli/src/exchange.rs	Removes an unused import (no behavior change).
scripts/multisig-e2e-test.sh	New end-to-end script covering export/sign/submit against a live sequencer, including negative-path assertions.
.github/workflows/ci.yml	Adds a new CI job to run the multisig E2E script using the existing LEZ setup/caching approach.

Review details

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Lite

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