fix(cargo-gamma): stabilize builds and output handling

- Stabilize staged workspace builds. Keep a constant whole-workspace Cargo root set when the resolved selection covers every member, while limiting mutation blame and rollback to the current stage. This prevents dependency feature changes from repeatedly compiling new variants.

- Make build-output capture robust. Raise each Cargo stream limit from 4 MiB to 256 MiB and each logical-line limit from 64 KiB to 1 MiB, while growing buffers on demand instead of reserving the ceiling up front.

- Normalize Cargo progress rendering. Consume Cargo's leading ANSI erase-to-end-of-line sequence so redirected or non-ANSI displays do not print a literal `\e[K`.

- Remove the containment startup warning. Hosts without delegated cgroups still use the existing best-effort process-group fallback, but cargo-gamma no longer emits the noisy warning.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot-Session: 6ca9796b-96b2-41c1-b138-4ecbb21aac02

Author: Martin Taillefer

Cargo.lock

@@ -34,12 +34,12 @@ bytes = { version = "1.12.1", default-features = false }
 camino = { version = "1.2.5", default-features = false }
 # local dependencies
 cargo-aprz-lib = { path = "crates/cargo-aprz-lib", default-features = false, version = "1.1.2" }
-cargo-gamma-attrs-impl = { path = "crates/cargo-gamma-attrs-impl", default-features = false, version = "0.2.0" }
-cargo-gamma-engine = { path = "crates/cargo-gamma-engine", default-features = false, version = "0.2.0" }
-cargo-gamma-lib = { path = "crates/cargo-gamma-lib", default-features = false, version = "0.2.0" }
-cargo-gamma-process = { path = "crates/cargo-gamma-process", default-features = false, version = "0.2.0" }
-cargo-gamma-rt = { path = "crates/cargo-gamma-rt", default-features = false, version = "0.2.0" }
-cargo-gamma-unsafe = { path = "crates/cargo-gamma-unsafe", default-features = false, version = "0.2.0" }
+cargo-gamma-attrs-impl = { path = "crates/cargo-gamma-attrs-impl", default-features = false, version = "0.2.1" }
+cargo-gamma-engine = { path = "crates/cargo-gamma-engine", default-features = false, version = "0.2.1" }
+cargo-gamma-lib = { path = "crates/cargo-gamma-lib", default-features = false, version = "0.2.1" }
+cargo-gamma-process = { path = "crates/cargo-gamma-process", default-features = false, version = "0.2.1" }
+cargo-gamma-rt = { path = "crates/cargo-gamma-rt", default-features = false, version = "0.2.1" }
+cargo-gamma-unsafe = { path = "crates/cargo-gamma-unsafe", default-features = false, version = "0.2.1" }
 cargo-heather = { path = "crates/cargo-heather", default-features = false, version = "0.2.1" }
 # external dependencies
 cargo-platform = { version = "0.3.3", default-features = false }

Cargo.toml

@@ -4,7 +4,7 @@
 [package]
 name = "cargo-gamma-attrs-impl"
 description = "Implementation of the inert attribute macros exposed by cargo-gamma-attrs"
-version = "0.2.0"
+version = "0.2.1"
 readme = "README.md"
 keywords = ["cargo", "mutation-testing", "testing"]
 categories = ["development-tools::testing"]

crates/cargo-gamma-attrs-impl/Cargo.toml

@@ -4,7 +4,7 @@
 [package]
 name = "cargo-gamma-attrs"
 description = "Inert attribute macros for suppressing cargo-gamma mutations"
-version = "0.2.0"
+version = "0.2.1"
 readme = "README.md"
 keywords = ["cargo", "mutation-testing", "testing"]
 categories = ["development-tools::testing"]

crates/cargo-gamma-attrs/Cargo.toml

@@ -4,7 +4,7 @@
 [package]
 name = "cargo-gamma-engine"
 description = "Internal Rust source mutation engine for cargo-gamma"
-version = "0.2.0"
+version = "0.2.1"
 readme = "README.md"
 keywords = ["cargo", "mutation-testing", "testing"]
 categories = ["development-tools::testing"]

crates/cargo-gamma-engine/Cargo.toml

@@ -4,7 +4,7 @@
 [package]
 name = "cargo-gamma-lib"
 description = "Internal library for cargo-gamma"
-version = "0.2.0"
+version = "0.2.1"
 readme = "README.md"
 keywords = ["cargo", "mutation-testing", "testing"]
 categories = ["development-tools::testing"]

crates/cargo-gamma-lib/Cargo.toml

@@ -61,6 +61,24 @@ includes both failure to acquire the startup environment and a guard reached
 before the runtime constructor installed its selection; either fixed marker
 disqualifies the process as mutation-score evidence.
 
+Interactive build progress reuses Cargo's progress text while cargo-gamma owns
+the terminal redraw. Cargo's leading erase control is consumed rather than
+rendered visibly, and its color styling remains intact.
+
+Each Cargo output stream is retained up to 256 MiB for artifact and diagnostic
+processing, and each logical line is bounded at 1 MiB. The buffers grow with
+observed output rather than reserving those ceilings for every invocation.
+
+When Cargo's resolved package selection covers the whole workspace, every stage
+checks mutation viability with that constant Cargo root set. Packages with no
+mutable files may be omitted from preflight, but do not narrow the staged
+checks. This keeps dependency feature unification identical across stages
+instead of compiling a new dependency variant for each downstream package
+selection. Diagnostic blame, isolation, and withdrawal remain limited to the
+current stage even though Cargo checks the wider graph. The final test-target
+build retains its reachability-based package selection; runs whose original
+Cargo selection is a package subset retain their narrowed graph throughout.
+
 Diff paths are resolved to the workspace-relative Rust files discovered by the
 survey. Absolute or rooted paths inside the workspace are normalized to those
 candidates; one from another checkout is normalized only when its suffix