diff --git a/Cargo.lock b/Cargo.lock
index d4c1a02c018af..f931752071dda 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -25,7 +25,7 @@ checksum = "b169f7a6d4742236a0a00c541b845991d0ac43e546831af1249753ab4c3aa3a0"
 dependencies = [
  "cfg-if",
  "cipher",
- "cpufeatures",
+ "cpufeatures 0.2.17",
 ]
 
 [[package]]
@@ -565,6 +565,17 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
 
+[[package]]
+name = "chacha20"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6f8d983286843e49675a4b7a2d174efe136dc93a18d69130dd18198a6c167601"
+dependencies = [
+ "cfg-if",
+ "cpufeatures 0.3.0",
+ "rand_core 0.10.0",
+]
+
 [[package]]
 name = "chrono"
 version = "0.4.42"
@@ -892,6 +903,17 @@ dependencies = [
  "windows-sys 0.59.0",
 ]
 
+[[package]]
+name = "console"
+version = "0.16.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d64e8af5551369d19cf50138de61f1c42074ab970f74e99be916646777f8fc87"
+dependencies = [
+ "encode_unicode",
+ "libc",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "constant_time_eq"
 version = "0.3.1"
@@ -926,6 +948,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "cpufeatures"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8b2a41393f66f16b0823bb79094d54ac5fbd34ab292ddafb9a0456ac9f87d201"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "crc32fast"
 version = "1.5.0"
@@ -1585,10 +1616,24 @@ checksum = "26145e563e54f2cadc477553f1ec5ee650b00862f0a58bcd12cbdc5f0ea2d2f4"
 dependencies = [
  "cfg-if",
  "libc",
- "r-efi",
+ "r-efi 5.3.0",
  "wasi 0.14.2+wasi-0.2.4",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0de51e6874e94e7bf76d726fc5d13ba782deca734ff60d5bb2fb2607c7406555"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi 6.0.0",
+ "rand_core 0.10.0",
+ "wasip2",
+ "wasip3",
+]
+
 [[package]]
 name = "gimli"
 version = "0.31.1"
@@ -1968,13 +2013,24 @@ version = "0.17.11"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "183b3088984b400f4cfac3620d5e076c84da5364016b4f49473de574b2586235"
 dependencies = [
- "console",
+ "console 0.15.11",
  "number_prefix",
  "portable-atomic",
  "unicode-width 0.2.2",
  "web-time",
 ]
 
+[[package]]
+name = "indicatif"
+version = "0.18.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "25470f23803092da7d239834776d653104d551bc4d7eacaf31e6837854b8e9eb"
+dependencies = [
+ "console 0.16.3",
+ "portable-atomic",
+ "unit-prefix",
+]
+
 [[package]]
 name = "indoc"
 version = "1.0.9"
@@ -2999,9 +3055,9 @@ dependencies = [
 
 [[package]]
 name = "portable-atomic"
-version = "1.11.1"
+version = "1.13.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f84267b20a16ea918e43c6a88433c2d54fa145c92a811b5b047ccbe153674483"
+checksum = "c33a9471896f1c69cecef8d20cbe2f7accd12527ce60845ff44c153bb2a21b49"
 
 [[package]]
 name = "portable-atomic-util"
@@ -3074,6 +3130,16 @@ dependencies = [
  "owo-colors",
 ]
 
+[[package]]
+name = "prettyplease"
+version = "0.2.37"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "479ca8adacdd7ce8f1fb39ce9ecccbfe93a3f1344b3d0d97f20bc0196208f62b"
+dependencies = [
+ "proc-macro2",
+ "syn 2.0.110",
+]
+
 [[package]]
 name = "proc-macro-hack"
 version = "0.5.20+deprecated"
@@ -3163,6 +3229,12 @@ version = "5.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "69cdb34c158ceb288df11e18b4bd39de994f6657d83847bdffdbd7f346754b0f"
 
+[[package]]
+name = "r-efi"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
+
 [[package]]
 name = "rancor"
 version = "0.1.1"
@@ -3193,6 +3265,17 @@ dependencies = [
  "rand_core 0.9.3",
 ]
 
+[[package]]
+name = "rand"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bc266eb313df6c5c09c1c7b1fbe2510961e5bcd3add930c1e31f7ed9da0feff8"
+dependencies = [
+ "chacha20",
+ "getrandom 0.4.2",
+ "rand_core 0.10.0",
+]
+
 [[package]]
 name = "rand_chacha"
 version = "0.3.1"
@@ -3213,6 +3296,16 @@ dependencies = [
  "rand_core 0.9.3",
 ]
 
+[[package]]
+name = "rand_chacha"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3e6af7f3e25ded52c41df4e0b1af2d047e45896c2f3281792ed68a1c243daedb"
+dependencies = [
+ "ppv-lite86",
+ "rand_core 0.10.0",
+]
+
 [[package]]
 name = "rand_core"
 version = "0.6.4"
@@ -3231,6 +3324,12 @@ dependencies = [
  "getrandom 0.3.3",
 ]
 
+[[package]]
+name = "rand_core"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0c8d0fd677905edcbeedbf2edb6494d676f0e98d54d5cf9bda0b061cb8fb8aba"
+
 [[package]]
 name = "rand_xorshift"
 version = "0.4.0"
@@ -5209,7 +5308,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e3bf829a2d51ab4a5ddf1352d8470c140cadc8301b2ae1789db023f01cedd6ba"
 dependencies = [
  "cfg-if",
- "cpufeatures",
+ "cpufeatures 0.2.17",
  "digest",
 ]
 
@@ -5220,7 +5319,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a7507d819769d01a365ab707794a4084392c824f54a7a6a7862f8c3d0892b283"
 dependencies = [
  "cfg-if",
- "cpufeatures",
+ "cpufeatures 0.2.17",
  "digest",
 ]
 
@@ -5531,10 +5630,10 @@ checksum = "8f50febec83f5ee1df3015341d8bd429f2d1cc62bcba7ea2076759d315084683"
 name = "test-float-parse"
 version = "0.1.0"
 dependencies = [
- "indicatif",
+ "indicatif 0.18.4",
  "num",
- "rand 0.9.2",
- "rand_chacha 0.9.0",
+ "rand 0.10.0",
+ "rand_chacha 0.10.0",
  "rayon",
 ]
 
@@ -5946,7 +6045,7 @@ dependencies = [
  "colored 3.0.0",
  "comma",
  "crossbeam-channel",
- "indicatif",
+ "indicatif 0.17.11",
  "levenshtein",
  "prettydiff",
  "regex",
@@ -6083,6 +6182,12 @@ dependencies = [
  "diff",
 ]
 
+[[package]]
+name = "unit-prefix"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "81e544489bf3d8ef66c953931f56617f423cd4b5494be343d9b9d3dda037b9a3"
+
 [[package]]
 name = "unstable-book-gen"
 version = "0.1.0"
@@ -6202,6 +6307,24 @@ version = "40.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bb5e2b9858989c3a257de4ca169977f4f79897b64e4f482f188f4fcf8ac557d1"
 
+[[package]]
+name = "wasip2"
+version = "1.0.2+wasi-0.2.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9517f9239f02c069db75e65f174b3da828fe5f5b945c4dd26bd25d89c03ebcf5"
+dependencies = [
+ "wit-bindgen",
+]
+
+[[package]]
+name = "wasip3"
+version = "0.4.0+wasi-0.3.0-rc-2026-01-06"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5428f8bf88ea5ddc08faddef2ac4a67e390b88186c703ce6dbd955e1c145aca5"
+dependencies = [
+ "wit-bindgen",
+]
+
 [[package]]
 name = "wasm-bindgen"
 version = "0.2.105"
@@ -6264,8 +6387,8 @@ dependencies = [
  "wat",
  "windows-sys 0.61.2",
  "winsplit",
- "wit-component",
- "wit-parser",
+ "wit-component 0.245.1",
+ "wit-parser 0.245.1",
 ]
 
 [[package]]
@@ -6285,6 +6408,16 @@ dependencies = [
  "wasmparser 0.219.2",
 ]
 
+[[package]]
+name = "wasm-encoder"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "990065f2fe63003fe337b932cfb5e3b80e0b4d0f5ff650e6985b1048f62c8319"
+dependencies = [
+ "leb128fmt",
+ "wasmparser 0.244.0",
+]
+
 [[package]]
 name = "wasm-encoder"
 version = "0.245.1"
@@ -6295,6 +6428,18 @@ dependencies = [
  "wasmparser 0.245.1",
 ]
 
+[[package]]
+name = "wasm-metadata"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb0e353e6a2fbdc176932bbaab493762eb1255a7900fe0fea1a2f96c296cc909"
+dependencies = [
+ "anyhow",
+ "indexmap",
+ "wasm-encoder 0.244.0",
+ "wasmparser 0.244.0",
+]
+
 [[package]]
 name = "wasm-metadata"
 version = "0.245.1"
@@ -6327,6 +6472,18 @@ dependencies = [
  "indexmap",
 ]
 
+[[package]]
+name = "wasmparser"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47b807c72e1bac69382b3a6fb3dbe8ea4c0ed87ff5629b8685ae6b9a611028fe"
+dependencies = [
+ "bitflags",
+ "hashbrown 0.15.5",
+ "indexmap",
+ "semver",
+]
+
 [[package]]
 name = "wasmparser"
 version = "0.245.1"
@@ -6771,6 +6928,26 @@ version = "0.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3ab703352da6a72f35c39a533526393725640575bb211f61987a2748323ad956"
 
+[[package]]
+name = "wit-bindgen"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d7249219f66ced02969388cf2bb044a09756a083d0fab1e566056b04d9fbcaa5"
+dependencies = [
+ "wit-bindgen-rust-macro",
+]
+
+[[package]]
+name = "wit-bindgen-core"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea61de684c3ea68cb082b7a88508a8b27fcc8b797d738bfc99a82facf1d752dc"
+dependencies = [
+ "anyhow",
+ "heck 0.5.0",
+ "wit-parser 0.244.0",
+]
+
 [[package]]
 name = "wit-bindgen-rt"
 version = "0.39.0"
@@ -6780,6 +6957,56 @@ dependencies = [
  "bitflags",
 ]
 
+[[package]]
+name = "wit-bindgen-rust"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b7c566e0f4b284dd6561c786d9cb0142da491f46a9fbed79ea69cdad5db17f21"
+dependencies = [
+ "anyhow",
+ "heck 0.5.0",
+ "indexmap",
+ "prettyplease",
+ "syn 2.0.110",
+ "wasm-metadata 0.244.0",
+ "wit-bindgen-core",
+ "wit-component 0.244.0",
+]
+
+[[package]]
+name = "wit-bindgen-rust-macro"
+version = "0.51.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0c0f9bfd77e6a48eccf51359e3ae77140a7f50b1e2ebfe62422d8afdaffab17a"
+dependencies = [
+ "anyhow",
+ "prettyplease",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.110",
+ "wit-bindgen-core",
+ "wit-bindgen-rust",
+]
+
+[[package]]
+name = "wit-component"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9d66ea20e9553b30172b5e831994e35fbde2d165325bec84fc43dbf6f4eb9cb2"
+dependencies = [
+ "anyhow",
+ "bitflags",
+ "indexmap",
+ "log",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "wasm-encoder 0.244.0",
+ "wasm-metadata 0.244.0",
+ "wasmparser 0.244.0",
+ "wit-parser 0.244.0",
+]
+
 [[package]]
 name = "wit-component"
 version = "0.245.1"
@@ -6794,9 +7021,27 @@ dependencies = [
  "serde_derive",
  "serde_json",
  "wasm-encoder 0.245.1",
- "wasm-metadata",
+ "wasm-metadata 0.245.1",
  "wasmparser 0.245.1",
- "wit-parser",
+ "wit-parser 0.245.1",
+]
+
+[[package]]
+name = "wit-parser"
+version = "0.244.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ecc8ac4bc1dc3381b7f59c34f00b67e18f910c2c0f50015669dde7def656a736"
+dependencies = [
+ "anyhow",
+ "id-arena",
+ "indexmap",
+ "log",
+ "semver",
+ "serde",
+ "serde_derive",
+ "serde_json",
+ "unicode-xid",
+ "wasmparser 0.244.0",
 ]
 
 [[package]]
diff --git a/Cargo.toml b/Cargo.toml
index 67c7a9d67edc8..dd0d5841441fb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -77,7 +77,8 @@ strip = true
 debug = 0
 strip = true
 
-# Bigint libraries are slow without optimization, speed up testing
+# Bigint libraries are slow without optimization, speed up testing. Note that this doesn't affect
+# its dependencies, it should still be run in release mode where possible.
 [profile.dev.package.test-float-parse]
 opt-level = 3
 
@@ -92,4 +93,3 @@ codegen-units = 1
 # If you want to use a crate with local modifications, you can set a path or git dependency here.
 # For git dependencies, also add your source to ALLOWED_SOURCES in src/tools/tidy/src/extdeps.rs.
 #[patch.crates-io]
-
diff --git a/src/bootstrap/src/utils/proc_macro_deps.rs b/src/bootstrap/src/utils/proc_macro_deps.rs
index fee9b12aca069..8472c61f82c3c 100644
--- a/src/bootstrap/src/utils/proc_macro_deps.rs
+++ b/src/bootstrap/src/utils/proc_macro_deps.rs
@@ -3,9 +3,12 @@
 /// See <https://github.com/rust-lang/rust/issues/134863>
 pub static CRATES: &[&str] = &[
     // tidy-alphabetical-start
+    "allocator-api2",
+    "anyhow",
     "askama_derive",
     "askama_parser",
     "basic-toml",
+    "bitflags",
     "block-buffer",
     "bumpalo",
     "cfg-if",
@@ -24,24 +27,32 @@ pub static CRATES: &[&str] = &[
     "generic-array",
     "hashbrown",
     "heck",
+    "id-arena",
     "ident_case",
     "indexmap",
     "intl-memoizer",
     "intl_pluralrules",
+    "itoa",
+    "leb128fmt",
     "libc",
+    "log",
     "memchr",
     "minimal-lexical",
     "nom",
     "pest",
     "pest_generator",
     "pest_meta",
+    "prettyplease",
     "proc-macro2",
     "quote",
     "rustc-hash",
+    "ryu",
     "self_cell",
+    "semver",
     "serde",
     "serde_core",
     "serde_derive_internals",
+    "serde_json",
     "sha2",
     "smallvec",
     "stable_deref_trait",
@@ -57,10 +68,18 @@ pub static CRATES: &[&str] = &[
     "unic-langid-impl",
     "unic-langid-macros",
     "unicode-ident",
+    "unicode-xid",
     "version_check",
     "wasm-bindgen-macro-support",
     "wasm-bindgen-shared",
+    "wasm-encoder",
+    "wasm-metadata",
+    "wasmparser",
     "winnow",
+    "wit-bindgen-core",
+    "wit-bindgen-rust",
+    "wit-component",
+    "wit-parser",
     "yoke",
     "zerofrom",
     "zerovec",
diff --git a/src/tools/test-float-parse/Cargo.toml b/src/tools/test-float-parse/Cargo.toml
index e407e322f9e19..5208b1eee9393 100644
--- a/src/tools/test-float-parse/Cargo.toml
+++ b/src/tools/test-float-parse/Cargo.toml
@@ -5,11 +5,11 @@ edition = "2024"
 publish = false
 
 [dependencies]
-indicatif = { version = "0.17.8", default-features = false }
+indicatif = { version = "0.18.4", default-features = false }
 num = "0.4.3"
-rand = "0.9.0"
-rand_chacha = "0.9.0"
-rayon = "1"
+rand = "0.10.0"
+rand_chacha = "0.10.0"
+rayon = "1.11.0"
 
 [lib]
 name = "test_float_parse"
diff --git a/src/tools/test-float-parse/build.rs b/src/tools/test-float-parse/build.rs
new file mode 100644
index 0000000000000..dbb56dc781b71
--- /dev/null
+++ b/src/tools/test-float-parse/build.rs
@@ -0,0 +1,9 @@
+use std::env;
+
+fn main() {
+    // Forward the opt level so we can warn if the tests are going to be slow.
+    let opt = env::var("OPT_LEVEL").expect("OPT_LEVEL unset");
+    let profile = env::var("PROFILE").expect("PROFILE unset");
+    println!("cargo::rustc-env=OPT_LEVEL={opt}");
+    println!("cargo::rustc-env=PROFILE={profile}");
+}
diff --git a/src/tools/test-float-parse/src/gen_/fuzz.rs b/src/tools/test-float-parse/src/gen_/fuzz.rs
index 1d6c5562a14c8..f5917c081c6e9 100644
--- a/src/tools/test-float-parse/src/gen_/fuzz.rs
+++ b/src/tools/test-float-parse/src/gen_/fuzz.rs
@@ -5,7 +5,7 @@ use std::marker::PhantomData;
 use std::ops::Range;
 use std::sync::Mutex;
 
-use rand::Rng;
+use rand::RngExt;
 use rand::distr::{Distribution, StandardUniform};
 use rand_chacha::ChaCha8Rng;
 use rand_chacha::rand_core::SeedableRng;
@@ -62,7 +62,7 @@ where
     }
 
     fn new() -> Self {
-        let rng = ChaCha8Rng::from_seed(SEED);
+        let rng = ChaCha8Rng::from_seed(SEED.0);
 
         Self { iter: 0..Self::total_tests(), rng, marker: PhantomData }
     }
diff --git a/src/tools/test-float-parse/src/gen_/many_digits.rs b/src/tools/test-float-parse/src/gen_/many_digits.rs
index 741e11437fe29..bec70f93d001e 100644
--- a/src/tools/test-float-parse/src/gen_/many_digits.rs
+++ b/src/tools/test-float-parse/src/gen_/many_digits.rs
@@ -4,7 +4,7 @@ use std::marker::PhantomData;
 use std::ops::{Range, RangeInclusive};
 
 use rand::distr::{Distribution, Uniform};
-use rand::{Rng, SeedableRng};
+use rand::{RngExt, SeedableRng};
 use rand_chacha::ChaCha8Rng;
 
 use crate::{Float, Generator, SEED};
@@ -39,7 +39,7 @@ impl<F: Float> Generator<F> for RandDigits<F> {
     }
 
     fn new() -> Self {
-        let rng = ChaCha8Rng::from_seed(SEED);
+        let rng = ChaCha8Rng::from_seed(SEED.0);
         let range = Uniform::try_from(0..10).unwrap();
 
         Self { rng, iter: 0..ITERATIONS, uniform: range, marker: PhantomData }
diff --git a/src/tools/test-float-parse/src/lib.rs b/src/tools/test-float-parse/src/lib.rs
index da83aeea3c132..278396ca4e1dd 100644
--- a/src/tools/test-float-parse/src/lib.rs
+++ b/src/tools/test-float-parse/src/lib.rs
@@ -10,11 +10,13 @@ use std::any::type_name;
 use std::cmp::min;
 use std::ops::RangeInclusive;
 use std::process::ExitCode;
-use std::sync::OnceLock;
 use std::sync::atomic::{AtomicU64, Ordering};
-use std::{fmt, time};
+use std::sync::{LazyLock, OnceLock};
+use std::{env, fmt, time};
 
+use rand::TryRng;
 use rand::distr::{Distribution, StandardUniform};
+use rand::rngs::SysRng;
 use rayon::prelude::*;
 use time::{Duration, Instant};
 use traits::{Float, Generator, Int};
@@ -44,8 +46,41 @@ const MAX_BITS_FOR_EXHAUUSTIVE: u32 = 32;
 /// `--skip-huge`.
 const HUGE_TEST_CUTOFF: u64 = 5_000_000;
 
-/// Seed for tests that use a deterministic RNG.
-const SEED: [u8; 32] = *b"3.141592653589793238462643383279";
+const SEED_ENV: &str = "TEST_FLOAT_PARSE_SEED";
+
+/// Seed for tests that use a deterministic RNG, and its b64 representation for printing. Taken
+/// from env if provided,
+static SEED: LazyLock<([u8; 32], Box<str>)> = LazyLock::new(|| {
+    let seed = match env::var(SEED_ENV) {
+        Ok(s) => {
+            seed_from_str(&s).unwrap_or_else(|| panic!("{SEED_ENV} must be 32 bytes, hex encoded"))
+        }
+        Err(_) => {
+            let mut seed = [0u8; 32];
+            SysRng.try_fill_bytes(&mut seed).unwrap();
+            seed
+        }
+    };
+
+    let lo = u128::from_le_bytes(seed[..16].try_into().unwrap());
+    let hi = u128::from_le_bytes(seed[16..].try_into().unwrap());
+    let encoded = format!("{hi:032x}{lo:032x}").into_boxed_str();
+
+    (seed, encoded)
+});
+
+fn seed_from_str(s: &str) -> Option<[u8; 32]> {
+    let hi = s.get(..32)?;
+    let hi = u128::from_str_radix(hi, 16).ok()?;
+    let lo = s.get(32..)?;
+    let lo = u128::from_str_radix(lo, 16).ok()?;
+
+    let mut out = [0u8; 32];
+    out[..16].copy_from_slice(&lo.to_le_bytes());
+    out[16..].copy_from_slice(&hi.to_le_bytes());
+
+    Some(out)
+}
 
 /// Global configuration.
 #[derive(Debug)]
@@ -78,8 +113,10 @@ pub fn run(cfg: Config, include: &[String], exclude: &[String]) -> ExitCode {
     let threads = std::thread::available_parallelism().map(Into::into).unwrap_or(0) * 3 / 2;
     rayon::ThreadPoolBuilder::new().num_threads(threads).build_global().unwrap();
 
+    println!("Starting test runner");
+    println!("Using {SEED_ENV}={}`", SEED.1);
     let mut tests = register_tests(&cfg);
-    println!("registered");
+    println!("Tests registered");
     let initial_tests: Vec<_> = tests.iter().map(|t| t.name.clone()).collect();
 
     let unmatched: Vec<_> = include
diff --git a/src/tools/test-float-parse/src/main.rs b/src/tools/test-float-parse/src/main.rs
index 9c6cad7324f74..c049c094fe6b4 100644
--- a/src/tools/test-float-parse/src/main.rs
+++ b/src/tools/test-float-parse/src/main.rs
@@ -39,12 +39,24 @@ enum ArgMode {
 }
 
 fn main() -> ExitCode {
-    if cfg!(debug_assertions) {
+    let opt = env!("OPT_LEVEL");
+    let profile = env!("PROFILE");
+
+    println!("Crate config:");
+    println!("    opt level: {opt}");
+    println!("    profile: {profile}");
+    println!("    debug assertions: {}", cfg!(debug_assertions));
+
+    if !matches!(opt, "2" | "3") || profile != "release" {
+        // Warn for `profile != release` because optimizations being on for this crate (always,
+        // via the workspace Cargo.toml)  may not mean they are on for dependencies.
         println!(
-            "WARNING: running in debug mode. Release mode is recommended to reduce test duration."
+            "WARNING: test-float-parse may be running unoptimized or with unoptimized \
+            dependencies. Release mode is recommended to reduce test duration."
         );
         std::thread::sleep(Duration::from_secs(2));
     }
+    println!("Running with debug assertions={}", cfg!(debug_assertions));
 
     let args: Vec<_> = std::env::args().skip(1).collect();
     if args.iter().any(|arg| arg == "--help" || arg == "-h") {
diff --git a/src/tools/test-float-parse/src/ui.rs b/src/tools/test-float-parse/src/ui.rs
index 1a9ba0dc1d99c..420f3f0bacd81 100644
--- a/src/tools/test-float-parse/src/ui.rs
+++ b/src/tools/test-float-parse/src/ui.rs
@@ -8,7 +8,7 @@ use std::time::Duration;
 
 use indicatif::{ProgressBar, ProgressStyle};
 
-use crate::{Completed, Config, EarlyExit, FinishedAll, TestInfo};
+use crate::{Completed, Config, EarlyExit, FinishedAll, SEED, SEED_ENV, TestInfo};
 
 /// Templates for progress bars.
 const PB_TEMPLATE: &str = "[{elapsed:3} {percent:3}%] {bar:20.cyan/blue} NAME \
@@ -135,6 +135,16 @@ pub fn finish_all(tests: &[TestInfo], total_elapsed: Duration, cfg: &Config) ->
     );
 
     if failed_generators > 0 || stopped_generators > 0 {
+        println!();
+        println!(
+            "ERROR: Some float parsing/printing tests failed.\n\
+            \n\
+            If you ever encounter this failure when not expected, PLEASE OPEN AN ISSUE!! The \
+            failure will likely go away on the next run, but may represent a real bug.\n\
+            \n\
+            To reproduce, rerun with the same seed: {}={}",
+            SEED_ENV, SEED.1
+        );
         ExitCode::FAILURE
     } else {
         ExitCode::SUCCESS