framework: make tool discoverability, workspace placement and model tiering mechanical (#1174)

packages/mosaic/framework/tools/git/test-mosaic-worktree-large-repo.sh

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+#!/usr/bin/env bash
+# test-mosaic-worktree-large-repo.sh — the helper must work on the repos it exists for.
+#
+# resolve_repo() took the first line of `git worktree list --porcelain` with
+# `awk '/^worktree /{print substr($0,10); exit}'`. The `exit` closes the read end
+# of the pipe while git is still writing, git takes SIGPIPE, and under
+# `set -euo pipefail` the command substitution returns 141 — so the assignment
+# fails, `set -e` aborts the function, and the script dies printing NOTHING. No
+# message, no path, no worktree, exit 141.
+#
+# What makes it worth a dedicated test rather than a fixture line is WHEN it
+# fires. If git finishes writing before awk leaves, there is no SIGPIPE and
+# everything works. So the failure is a function of how much porcelain the repo
+# produces: invisible on a three-worktree repo, reliable on a seventy-worktree
+# one. It was measured on a repo with 73 worktrees (10 KB of porcelain) — rc=141,
+# no output — and it had passed every hand-check before that, on small repos.
+#
+# A test that ran `git worktree list` against whatever repo it happens to sit in
+# would inherit that same size dependence and would have PASSED on the tree that
+# was broken. So git is stubbed on PATH and made to emit a large porcelain
+# stream, which turns "depends on the repo you are standing in" into "always".
+#
+# Exit: 0 = the helper resolved the repo · 1 = it did not
+
+set -uo pipefail
+
+HERE="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
+TOOL="${1:-$HERE/mosaic-worktree.sh}"
+[ -x "$TOOL" ] || { printf 'test-mosaic-worktree-large-repo: not executable: %s\n' "$TOOL" >&2; exit 2; }
+
+TMP="$(mktemp -d)"; trap 'rm -rf "$TMP"' EXIT
+mkdir -p "$TMP/bin"
+
+# The stub answers exactly the two calls resolve_repo makes, and answers the
+# porcelain one with ~450 KB — comfortably past a 64 KB pipe buffer, so the
+# writer is still writing when a reader that quits early goes away. Anything
+# else exits non-zero rather than pretending to be git.
+cat > "$TMP/bin/git" <<'STUB'
+#!/bin/sh
+while [ $# -gt 0 ]; do
+  case "$1" in -C) shift 2 ;; *) break ;; esac
+done
+case "$*" in
+  "rev-parse --git-dir")
+    echo .git; exit 0 ;;
+  "worktree list --porcelain")
+    # The first entry is the main worktree. That single line is all the helper
+    # needs, and it is exactly what it stopped receiving.
+    printf 'worktree /src/fakerepo\nHEAD %040d\nbranch refs/heads/main\n\n' 0
+    awk 'BEGIN{ for (i = 0; i < 4000; i++)
+                  printf "worktree /src/fakerepo-worktrees/w%d\nHEAD %040d\nbranch refs/heads/topic-%d\n\n", i, 0, i }'
+    # NOT `exit 0`. Real git dies of SIGPIPE here and reports 141, and pipefail
+    # in the caller is what turns that into the silent abort. A stub that exits 0
+    # regardless hands the caller a clean status and the probe passes on the
+    # broken tree — which is how this test failed to be a test on its first run.
+    exit $? ;;
+esac
+exit 1
+STUB
+chmod +x "$TMP/bin/git"
+
+fail=0
+check() {
+  local why="$1" want="$2" got="$3"
+  if [ "$want" = "$got" ]; then
+    printf 'ok    %s\n' "$why"
+  else
+    printf 'FAIL  %s\n        want: %s\n        got:  %s\n' "$why" "$want" "$got"
+    fail=1
+  fi
+}
+
+out="$(PATH="$TMP/bin:$PATH" "$TOOL" path feat/workspace-hygiene 2>&1)"
+rc=$?
+
+# Both halves are asserted. rc alone would pass if the helper started printing a
+# usage error, and output alone would miss a non-zero exit — and the defect's
+# signature is precisely a non-zero exit with no output, which only the pair
+# distinguishes from every other way this could go wrong.
+check 'resolving a repo with a large worktree list exits 0' 0 "$rc"
+check 'and derives the path from the main worktree' /src/fakerepo-worktrees/feat-workspace-hygiene "$out"
+
+printf '\n'
+if [ "$fail" -eq 0 ]; then
+  printf 'mosaic-worktree: resolves against a large porcelain stream.\n'
+else
+  cat <<'EOF'
+mosaic-worktree could not resolve the repository.
+
+An empty output with a non-zero exit is the SIGPIPE signature: a reader that
+quits early (`awk ... exit`, `head -n`) kills the producer, and pipefail turns
+that into a silent abort. Nothing in this script may close a git pipe early.
+EOF
+fi
+exit "$fail"