A3a/A3b ship a per-agent persona contract that the launcher composes from
process.env.MOSAIC_AGENT_CLASS (compose-contract -> readPersonaContractBlock,
launch.js). generateAgentEnv already writes MOSAIC_AGENT_CLASS to
agents/<name>.env, but start-agent-session.sh only re-exported
MOSAIC_AGENT_NAME into the pane snippet — never the class.
The pane inherits the tmux SERVER environment, not this script's env nor the
systemd unit's EnvironmentFile, so the class set in the .env was invisible
in-pane. The launcher then saw an undefined class and silently injected NO
persona contract: every fleet agent came up class-less while `fleet ps`
reported healthy. The comms block kept working only because it keys on
MOSAIC_AGENT_NAME (which IS re-exported).
Fix: re-export MOSAIC_AGENT_CLASS into PANE_SHELL_SNIPPET exactly as
MOSAIC_AGENT_NAME, %q-quoted (empty/unset class -> '' is a harmless no-op,
matching readPersonaContractBlock's empty-class contract). Verified live: a
relaunched agent now carries MOSAIC_AGENT_CLASS in its pane env and the
matching `# Persona Contract (<class>)` block in its composed prompt.
Adds a regression guard to test-start-agent-session.sh asserting the pane
snippet exports both MOSAIC_AGENT_NAME and the per-agent MOSAIC_AGENT_CLASS.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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