A child that streams megabytes without a newline grew LiveTail's partial
line (and the retained tail) without limit: 8MB of output kept ~25MB.
Keep only the last MAX_LINE characters of an over-long line; its end is
the informative part.
The streamed-backend-output test now runs in verbose mode: live backend
output is the verbose/CI contract, and quiet mode deliberately contains it.
uv, npm ci, icon generation and the desktop build printed hundreds of
lines on every interactive install, update and `hermes desktop`.
pm/progress.py holds one policy. CI (CI / GITHUB_ACTIONS) or
HERMES_VERBOSE=1 streams child output unchanged. Otherwise each child is
one "→ label…" line, rewritten in place with its latest output on a
terminal, or just the start and finish lines when piped. A failure
always prints the last 80 lines. HERMES_VERBOSE=0 forces containment.
Applied to PM's uv runs (no uv --verbose outside CI; quick steps stay
silent unless they fail), the source build scripts (node-deps, TUI,
icons, web; npm warn lines stay out of the live line), the desktop
build and package steps, and the Windows ARM64 vcpkg/OpenSSL provider.
The policy reads the parent's environment, so the CI=1 the builders
force on their node children does not switch it to verbose.
