Add Exponent Finance Solana visualizer preset

[kyle-anchorage]

Why this PR exists

Solana transactions calling the Exponent Finance core program (ExponentnaRg3CQbW6dqQNZKXp7gtZ9DGMp1cwC4HAS7) currently fall through to the generic unknown_program visualizer, so wallet sign prompts show only the program ID and raw hex instruction data. This adds a dedicated preset that surfaces the instruction name, named accounts, and decoded args.

What changed

• New preset crate module presets::exponent_finance registered under visualsign-solana.
• IDL JSON (exponent_finance.json) sourced from the published @exponent-labs/exponent-idl npm package, which is the same data the Exponent SDK and orbmarkets explorer ship.
• Standard generic-IDL scaffolding: decode_idl_data -> parse_instruction_with_idl -> build_named_accounts -> field builders, mirroring the dflow_aggregator preset.
• Visualizer kind: Dex ("Exponent Finance"). Config matches all instructions for the program ID via ("*", vec!["*"]).

Two adaptations relative to the standard Anchor-style scaffold:

• Exponent uses Anchor 0.31's #[instruction(discriminator = [N])] attribute, so on-chain instruction discriminators are 1 byte rather than 8. The minimum-data-length check is data.is_empty() and the idl_has_discriminators test only asserts !disc.is_empty(). The underlying solana_parser::find_instruction_by_discriminator already supports variable-length discriminators.
• The IDL's Number type is a tuple-struct (a single anonymous [u64; 4] field). solana_parser's IdlField schema requires named fields, so that one entry was rewritten in the JSON to {"name": "value", "type": {"array": ["u64", 4]}}. No other types or instructions were modified.

Why this is safe

• Read-only feature: the parser only reads transaction bytes and produces display fields. No signing, custody, or settlement code is touched.
• Backward compatible: adds a new preset module and a single registration line in presets/mod.rs. Existing presets are unaffected. Programs that don't match the Exponent program ID continue to dispatch to their existing visualizer.
• Failure mode is graceful: if a future Exponent instruction has an unrecognized 1-byte discriminator, parse_exponent_finance_instruction returns Err, and the visualizer falls through to build_fallback_fields (which still emits the raw hex). This matches the dflow_aggregator pattern.
• The Number IDL patch is a structural rename only; the underlying type expression {"array": ["u64", 4]} is preserved, so any instruction that references Number will still decode the same bytes.

Checks run (by agent)

• cargo fmt -p visualsign-solana
• cargo clippy -p visualsign-solana --all-targets -- -D warnings -> clean
• cargo test -p visualsign-solana -> 70 unit tests pass (including the 4 new exponent_finance tests: idl_loads, idl_has_discriminators, unknown_discriminator_returns_error, short_data_returns_error)
• make -C src test -> all workspace tests pass
• make -C src lint -> clean across all crates

Manual steps needed (by human)

None - fully automated by CI.

How this is maintainable

• The preset follows the same shape as dflow_aggregator, so a developer touching either picks up the pattern from one place. The two deviations (1-byte discriminator handling and the Number-type rewrite) are documented inline by the test names and at the top of this PR.
• build.rs auto-discovers ExponentFinanceVisualizer from the new directory, so adding/removing presets doesn't require touching a registry.
• The IDL JSON is sourced from the upstream @exponent-labs/exponent-idl package; refreshing the IDL is a copy-paste of a new release plus re-applying the Number-field rewrite (the test test_exponent_finance_idl_loads will fail loudly if the rewrite is missed).
• Workspace lint policy (unwrap_used = "deny", etc.) is enforced - the preset uses ? and ok_or/ok_or_else for all fallible paths.
• The 4 sanity tests guard the discriminator/IDL contract: any future change that breaks IDL load, drops a discriminator, or stops rejecting empty/garbage input will surface in CI.

[Copilot]

Pull request overview

Adds a dedicated Solana visualizer preset for the Exponent Finance core program so transactions no longer fall back to the generic unknown_program rendering and instead show decoded instruction names, named accounts, and decoded arguments using the bundled IDL.

Changes:

• Registered a new presets::exponent_finance module under visualsign-solana.
• Implemented an IDL-driven instruction parser/visualizer (matching the existing generic-IDL scaffold pattern used by other presets).
• Added the Exponent Finance IDL JSON (with the documented Number struct field naming adaptation) and a program config mapping for dispatch.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
src/chain_parsers/visualsign-solana/src/presets/mod.rs	Registers the new exponent_finance preset module.
src/chain_parsers/visualsign-solana/src/presets/exponent_finance/mod.rs	Implements the Exponent Finance IDL-backed visualizer, parsing, field building, and unit tests.
src/chain_parsers/visualsign-solana/src/presets/exponent_finance/config.rs	Adds Solana integration config mapping the Exponent program ID to all instructions.
src/chain_parsers/visualsign-solana/src/presets/exponent_finance/exponent_finance.json	Bundles the Exponent Finance IDL used for decoding instruction discriminators/args/accounts.

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[prasanna-anchorage]

Approving. Rebased onto current main — the diff was reverting #284's pub mod kamino_limit; registration because the PR predates that merge. Resolved the presets/mod.rs conflict by keeping both exponent_finance and kamino_limit in alphabetical order.

Verification:

• cargo clippy -p visualsign-solana --all-targets -- -D warnings: clean.
• 4 exponent_finance preset tests pass (test_exponent_finance_idl_loads, test_exponent_finance_idl_has_discriminators, test_unknown_discriminator_returns_error, test_short_data_returns_error).
• Same preset template as the 11 other Kyle-authored Solana presets already on main.

config.rs uses HashMap per the current convention — #288's sweep will flip it to BTreeMap when that PR lands.