Moving to Hopper 0.4

Upgrade hopper-lang and the CLI together. The facade pins its matching hopper-derive version because generated code uses facade/runtime APIs from that release. The 0.4 line prevents existing 0.3 dependency ranges from selecting these new expansions.

hopper = { package = "hopper-lang", version = "=0.4.0", features = ["proc-macros"] }

Existing generated wire formats, discriminator bytes, layout fingerprints, positional constructors, and borrow APIs remain unchanged. Review these source and validation changes when upgrading:

• State macros generate a <State>Fields companion and from_fields / set_fields methods. Rename handwritten items that collide with those names. See named initialization for fixed-head and lifecycle limits.
• Handwritten body-only implementations of the legacy HopperLayout trait should set OVERLAY_OFFSET = 16. Its default remains zero for structs that include the account header. Generated state types set this automatically.
• Incorrect FixedLayout::SIZE implementations now fail during code generation on checked casts and collections. Leave the default or use the actual Rust type size. Overriding _SIZE_IS_HONEST does not bypass the check. cargo check alone does not exercise all generic compile-time assertions; run a build.
• Runtime typed loaders independently bound the actual type, even with custom validators and reported-size methods. Compact initialization rejects tail prefixes overlapping the head or overflowing their offset calculation.
• Typed segment descriptors must report the correct element size, count no greater than capacity, and an allocated region within the account. Previously accepted malformed metadata is rejected.
• The SOL vault example's deposit account list now includes the System Program. Clients of that example must supply it. This corrects its CPI account list; it does not automatically change other programs' instruction interfaces.

VerifiedAccount remains a size-checked overlay wrapper; its public constructors do not establish ownership or authorization. Use the appropriate account loader. The host harness remains a direct invocation tool: use compiled SBF and devnet tests for actual transaction rollback and custody rules.