refactor: split shim library and binary

[suzuke]

Implements task22 / issue #30: moves production shim into src/lib.rs with public shim_entry and leaves src/main.rs as a thin binary caller. Updates source invariants to audit lib.rs. Validation: focused tests, clippy, release build, diff check. Task22 scope only; no Cargo.toml or unrelated changes.

[suzuke]

VERIFIED — root exact-head review of 47bb3ea against task22 and d-20260713005740094423-4.

Evidence

• ran: normalized origin/main src/main.rs (fn main → pub fn shim_entry) SHA-256 = b8548d66dd78a3e71b7c898e0a6180790afc8c3aaa7c998ec45b861cce446e5f; HEAD src/lib.rs SHA-256 is byte-identical.
• cited: crates/agentic-git/src/main.rs — thin binary contains only agentic_git::shim_entry();.
• ran: cargo test --workspace → lib 156/156, bin 0/0, all non-ignored integration suites pass.
• ran: cargo clippy --workspace --all-targets -- -D warnings → pass.
• ran: cargo build --workspace --release → pass.
• ran: git diff --check origin/main...HEAD and tracked git diff --quiet → pass.
• inspected: exactly lib.rs, thin main.rs, and source-path-only changes in exec_reachability_invariant.rs/shim_phase2.rs; Cargo.toml and unrelated modules unchanged.

scope_source: task t-20260713005800717233-15764-22 + decision d-20260713005740094423-4
audit_mode: full exact-head behavioral-parity review
reviewed_head: 47bb3ea
files: crates/agentic-git/src/{lib.rs,main.rs}, crates/agentic-git/tests/{exec_reachability_invariant.rs,shim_phase2.rs}

No blocking findings. Independent Fable review and final CI merge gate remain required.

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codex-125550 · Codex GPT-5

[suzuke]

VERIFIED — exact head 47bb3ea (independent heterogeneous review, seat claude-aef7c0/Fable, task t-20260713211816327397-70517-156, review_class=dual; all evidence gathered independently, no reliance on prior review comments or implementer claims)

Scope matches the frozen d-4/task22 boundary exactly: 4 files, entrypoint-only source delta, no manifest drift.

Evidence

• ran: git show 4a0022eb:crates/agentic-git/src/main.rs | diff - crates/agentic-git/src/lib.rs → single-line delta at :128 fn main() { → pub fn shim_entry() {; the remaining 3,283 lines are byte-identical. New src/main.rs is 3 lines calling agentic_git::shim_entry().
• ran: git diff --stat 4a0022eb..HEAD → exactly 4 files (src/lib.rs, src/main.rs, tests/exec_reachability_invariant.rs, tests/shim_phase2.rs). Cargo.toml/Cargo.lock untouched; crate manifest has no [lib]/[[bin]] sections, so cargo auto-discovery covers both targets — "no manifest change" holds.
• invariant enforcement preserved with NO blind spot: scan_crate_src() recursively walks all of src/ (exec_reachability_invariant.rs:306-315, fail-loud if empty), so the thin main.rs remains in the scan basis. Empirical: injected a decoy fn exec_real_git() {} into the thin main.rs → invariant went RED with UNEXPECTED (x1): main.rs :: <top-level> :: def exec_real_git; reverted, tracked tree clean at exact head. Whitelist + RED-arm label rewrites (main.rs→lib.rs) are exactly what the directory walk produces.
• ran: cargo test (workspace) → lib unittests 156 passed / 0 failed (suite runs ONCE via the library); bin unittests running 0 tests (bin harness zero — the duplicate-suite failure mode d-4 rejected is confirmed absent); all integration suites green (exec-invariant 8, shim_phase2 13+4 ignored, snapshots 24, session_mode 18, smoke 5, recursion-guard 2, phase1 5; stress suites ignored-by-default); agentic-git-core 10/10.
• ran: cargo clippy --workspace --all-targets -- -D warnings → clean (strict superset of CI's --workspace); cargo build --release -p agentic-git → PASS.
• ran (release binary, argv0 dual-mode): direct invocation → session CLI usage output; argv0=git symlink with agent env unset → non-agent passthrough, output byte-identical to /usr/bin/git --version. argv0 dispatch reads process-global env::args, unaffected by the split.
• CI at exact head: all 4 checks green (test ubuntu/macos, test-windows-advisory, legacy-env-adoption).
• tracked cleanliness: tracked state byte-clean after all runs; the only untracked path is the daemon-owned .agend-managed session binding marker at the worktree root — fleet infrastructure, not PR dirt, and irrelevant to cargo packaging (which operates under crates/).