release-fast profile

Introduces a `release-fast` profile that inherits from `release` but
uses thin LTO and 8 codegen units instead of full LTO + 1, cutting
link time significantly while remaining fast enough for integration
testing. Documents usage in CONTRIBUTING.md.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

CONTRIBUTING.md

@@ -56,6 +56,16 @@ Tests that require a real LLM key will skip gracefully if the env var is absent.
 cargo build --workspace
 ```
 
+### Fast Release Build (for development)
+
+The default `--release` profile uses full LTO and single-codegen-unit, which produces the smallest/fastest binary but is slow to compile. For iterating locally, use the `release-fast` profile instead:
+
+```bash
+cargo build --profile release-fast -p openfang-cli
+```
+
+This cuts link time significantly (thin LTO, 8 codegen units, `opt-level=2`) while still producing a binary fast enough to run integration tests against. Use `--release` only for final binaries or CI.
+
 ### Run All Tests
 
 ```bash

Cargo.toml

@@ -150,3 +150,10 @@ lto = true
 codegen-units = 1
 strip = true
 opt-level = 3
+
+[profile.release-fast]
+inherits = "release"
+lto = "thin"
+codegen-units = 8
+opt-level = 2
+strip = false