Malformed hook stdout that looks like JSON was collapsing into low-signal failure text during hook execution. This change preserves plain-text hook feedback for normal text hooks, but upgrades malformed JSON-like output into an explicit hook_invalid_json diagnostic that includes phase, tool, command, and bounded stdout/stderr previews. It also adds a regression test for malformed-but-nonempty output.
Constraint: User scoped the implementation to rust/crates/runtime/src/hooks.rs and tests only
Constraint: Existing plain-text hook feedback must remain intact for non-JSON hook output
Rejected: Treat every non-JSON stdout payload as invalid JSON | would break legitimate plain-text hook feedback
Confidence: high
Scope-risk: narrow
Directive: Keep malformed-hook diagnostics bounded and preserve the plain-text fallback for hooks that intentionally emit text
Tested: cargo test --manifest-path rust/Cargo.toml -p runtime hooks::tests:: -- --nocapture
Tested: cargo test --manifest-path rust/Cargo.toml -p runtime -- --nocapture
Tested: cargo clippy --manifest-path rust/Cargo.toml -p runtime --all-targets -- -D warnings
Not-tested: Full workspace clippy/test sweep outside runtime crate
e874bc6a44