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The two fixes from the 0.11 dogfood run. Version stays 0.12.0 here; the bump to 0.12.1 is the release's job. Draft: not for merge until reviewed.

F1: live verify names the verifier

probbit live verify printed the strand header's engine alone, so after an upgrade a strand written by the old engine read as if the old engine were still installed.

• The success summary keeps engine (the header's, the engine that wrote the strand) and adds verified_by (the engine that replayed it). Every other key and the exit codes are unchanged.
• Updated to match: docs/persona.md §5.7, docs/agents.md (probbit_live_verify row), the MCP tool description, python/probbit.py live_verify docstring.
• python/probbit_host.py receipts: when the verify answer has verified_by, the header line prints written by <engine>, verified by <verified_by>. bench/agentdojo/receipts-example.txt and the block in docs/receipts.md were regenerated with this branch's build; only the header line changed. The release should regenerate it after the bump, so it shows the released version.
• Test verify_names_the_writer_and_the_verifier: one strand written by the released 0.11.0 (a member of bench/agentdojo/tables/strands-A.tar.gz, committed as probbit-cli/tests/fixtures/strands/agentdojo-0.11.0.strand, 2,393 bytes) verifies with engine: "probbit 0.11.0" and verified_by: "probbit 0.12.0" (this engine). The existing 0.9.0-dev fixture test also asserts verified_by.

F2: the man page stays under the install prefix

install.sh wrote the man page to ~/.local/share/man/man1/ even when PROBBIT_INSTALL_DIR pointed somewhere else.

• PROBBIT_INSTALL_DIR=<prefix>/bin with no PROBBIT_MAN_DIR now installs it to <prefix>/share/man/man1/.
• Any other PROBBIT_INSTALL_DIR keeps the HOME default, and the installer's line now says the page went outside the install dir (PROBBIT_MAN_DIR to choose). PROBBIT_MAN_DIR still wins, and a failure is still not fatal.
• scripts/bench/test_install_sh.sh gains cases 6a (prefix/bin: the page is in the prefix, nothing under HOME) and 6a' (a dir that is not a bin dir: the page goes under HOME and the installer says so).
• The README install section, docs/CHEATSHEET.md, and probbit man's own text (help table, plus the committed docs/probbit.1) say where the page lands.
• install.ps1 installs no man page, so it is unchanged.

Tested where

All gates ran on a Linux x86_64 build node (Ubuntu 24.04, cargo 1.99.1). It ran one gate at a time and removed the target dir afterwards:

GATE test EXIT=0              cargo test --release --workspace --locked --no-fail-fast: 460 passed, 0 failed, 3 ignored (33 suites)
GATE build-release EXIT=0     cargo build --release --locked -p probbit-cli
GATE p0 EXIT=0                bench/individuality/p0.py check: 653 outputs, 0 differ, 8 strands verified
GATE install-contract EXIT=0  scripts/tests/test_install_contract.py
GATE install-sh EXIT=0        scripts/bench/test_install_sh.sh (sh, x86_64-unknown-linux-gnu): all checks passed, incl. 6a and 6a'
GATE python EXIT=0            python unittest with the new binary: 60 tests OK
GATE man-committed EXIT=0     probbit man == docs/probbit.1
GATE receipts EXIT=0          receipts regenerated; body identical to the committed example

macOS: python unittest only (60 OK), against the installed 0.12.0 binary.

Not tested here

• Windows and macOS builds and tests: CI covers them on this PR.
• cargo fmt and clippy: CI runs neither, and main is not rustfmt-formatted (cargo fmt --check on main reports 122,663 diff lines).