chore(release): Prepare 0.3.1

[Xuepoo]

Summary

Prepares the 0.3.1 release, covering the work merged since v0.3.0 (#9–#21).

Version bump

• Workspace version 0.3.0 → 0.3.1 in root Cargo.toml, including the two internal dep refs (ctx-symbol, ctx-exec)
• Cargo.lock local package versions refreshed via cargo check

Files changed

• Cargo.toml — workspace + internal dependency versions
• Cargo.lock — synced local package versions (ctx-symbol, ctx-exec, ctxctl)
• CHANGELOG.md — new [0.3.1] - 2026-08-24 entry

Highlights

Security

• mcp pins the workspace root and bounds spawned exec children with a wall-clock timeout (fix(mcp): Pin workspace root and bound exec children #15)
• exec rejects unquoted shell metacharacters with a sh -c hint (fix(exec): Reject unquoted shell metacharacters with sh -c hint #9)

Correctness

• Symbol: AST walk depth bound prevents stack overflow (fix(ctx-symbol): Bound AST walk depth to prevent stack overflow #11); preprocessor fold gated in Markdown backend, CRLF byte offsets fixed, C/C++ union kind added (fix(ctx-symbol): Gate preprocessor fold, add union kind, fix CRLF offsets #13)
• deps anchored to project root, ignore globs scoped to relative paths, explicit unresolved kind (fix(deps): Anchor resolution to project root and scope ignore globs to relative paths #18)

Robustness

• File guardrails: non-regular / oversized inputs refused up front (feat(cli): Refuse non-regular and oversized input files #16)
• exec: bounded pending buffer, passthrough byte fidelity, warning-trigger fix (fix(ctx-exec): Bound pending buffer, preserve passthrough bytes, correct warning trigger #17); empty-pattern rejection + validate-before-spawn (fix(exec): Reject empty keep patterns and validate options before spawn #12)
• Config tolerance: unreadable discovered configs skipped with warning (fix(config): Skip unreadable discovered configs with warning #21)

Contract fixes

• MCP: non-zero exec exits surfaced with matching exit codes; tool argument validation (fix(mcp): Surface non-zero exits and validate tool arguments #14)

Polish

• Backend dedup: shared helpers consolidated, signature caps/markers tightened, clap help aligned (refactor: Dedupe backend helpers and polish signature caps, markers, clap help #20); degenerate-input test corpus (test: Add degenerate-input corpus and MCP tool matrix #19)

Gates

• cargo fmt --check
• cargo clippy --all-features -- -D warnings
• cargo test — all suites pass