fix(ci): share l1-contracts solc across forge builds (#23347)

Point `barretenberg/sol` and `docs/examples/solidity` foundry configs at
`l1-contracts/solc-0.8.30` (the binary `l1-contracts/bootstrap.sh
download_solc` pulls in) instead of declaring their own solc versions.
Adds a `l1-contracts-solc` Makefile target so `bb-sol` and
`l1-contracts-src` depend on it explicitly; `docs` reaches it
transitively through `yarn-project → l1-contracts`. Eliminates the
parallel svm downloads that were racing on `~/.svm`.

Versions collapse from 0.8.29 / 0.8.27 / 0.8.30 onto 0.8.30 — pragmas in
both relocated projects already allow it (`>=0.8.21` / `>=0.8.27`).

Verified locally: `forge build` in `barretenberg/sol` and each
`docs/examples/solidity/*/` subdir reports `Compiling … with Solc
0.8.30` with no `~/.svm` activity.

---
*Created by
[claudebox](https://claudebox.work/v2/sessions/dee006170dffddb5) ·
group: `slackbot`*

Author: ludamad

Makefile

@@ -227,8 +227,11 @@ bb-acir: noir bb-cpp-native bb-ts
 bb-docs:
 	$(call build,$@,barretenberg/docs)
 
-# BB Solidity - Solidity verifier contracts
-bb-sol: bb-cpp-native bb-crs
+# BB Solidity - Solidity verifier contracts.
+# Depends on l1-contracts-solc so that the foundry build uses the solc binary
+# pulled in by l1-contracts (see barretenberg/sol/foundry.toml) rather than
+# triggering a parallel svm download.
+bb-sol: bb-cpp-native bb-crs l1-contracts-solc
 	$(call build,$@,barretenberg/sol)
 
 #==============================================================================
@@ -309,8 +312,16 @@ noir-projects: noir-protocol-circuits mock-protocol-circuits noir-contracts azte
 # L1 Contracts - Ethereum L1 smart contracts
 #==============================================================================
 
+# l1-contracts-solc: Download (or cache-hit) the pinned solc binary.
+# This is the single owner of the svm download. Other forge projects
+# (barretenberg/sol, docs/examples/solidity) point their foundry.toml at the
+# same binary, so they must wait on this target before invoking forge build,
+# otherwise parallel forge invocations race on ~/.svm.
+l1-contracts-solc:
+	$(call build,$@,l1-contracts,download_solc)
+
 # l1-contracts-src: Build all src/ contracts (fully independent!)
-l1-contracts-src:
+l1-contracts-src: l1-contracts-solc
 	$(call build,$@,l1-contracts,build_src)
 
 # l1-contracts-verifier: Build generated verifier and tests (depends on noir-protocol-circuits)

barretenberg/sol/foundry.toml

@@ -12,7 +12,10 @@ evm_version = "cancun"
 [fuzz]
 runs = 2
 
-solc = "0.8.29"
+# Use the pre-downloaded solc binary from l1-contracts. l1-contracts' build is
+# the single owner of the svm download; pointing other forge projects at the
+# same binary avoids parallel svm downloads racing on ~/.svm.
+solc = "../../l1-contracts/solc-0.8.30"
 
 [lint]
 ignore = ["./lib/**"]

docs/examples/solidity/foundry.toml

@@ -2,7 +2,10 @@
 src = '.'
 out = 'out'
 libs = ['../../../l1-contracts/lib', '../../../l1-contracts/src']
-solc_version = '0.8.27'
+# Use the pre-downloaded solc binary from l1-contracts. l1-contracts' build is
+# the single owner of the svm download; pointing other forge projects at the
+# same binary avoids parallel svm downloads racing on ~/.svm.
+solc = "../../../l1-contracts/solc-0.8.30"
 evm_version = 'prague'
 optimizer = true