fix(tmux): session env never reached the pane, so script agents ran blind

[ANonABento]

Found by running a script-runtime agent from a column for the first time — the MVP runtime that had never actually executed.

What already worked

argv, cwd and exit-code advancement were correct. The script received exactly --preset high --out cut.mp4, with no prose prompt appended, and a deliberately strict argument parser accepted it (ARGC: 4). #275's script handling held up: the column carried a stale cli: claude and runtime_mode: managed on purpose, and both were correctly ignored — the run resolved to terminal and executed the agent's own command.

What didn't

Every environment variable arrived unset:

PRESET: <unset>          THREADS: <unset>
TRIGGER_PROMPT: <unset>  WORKING_DIR: <unset>

Session environment was applied with Command::env on the tmux client. The tmux server is a pre-existing daemon, so new-session only asks it to create a session — the new shell inherits the server's environment, not the client's. Everything set that way was silently dropped.

That's also why the KAITENCODE_PARENT_* attribution variables are additionally inlined on the command line as KEY=val <cmd>: that workaround covered exactly those and nothing else.

Consequences: a script agent's configured env was inert while the dossier displayed it, and script agents received no prompt at all — not in argv (correctly; it would break strict parsers) and not in $TRIGGER_PROMPT. They ran context-free. My claim in #277 that the prompt rides $TRIGGER_PROMPT was true of the intent and false of the behaviour.

Fix

tmux new-session -e KEY=VAL sets it server-side and the pane inherits it, including values with spaces and =. Verified against tmux 3.4. Applied to both session-creation paths — the trigger one and the interactive one, which had the same bug.

Same run afterwards:

PRESET: fast             THREADS: 8
TRIGGER_PROMPT: Render the cut…   WORKING_DIR: …/worktrees/kaitencode-…
ARGV: --preset high --out cut.mp4     ARGC: 4     OK

Pipeline: Todo → Render → Done, exit 0, mode: terminal.

Test-artifact worth recording

Deleting a worktree out from under a live tmux session leaves the pane's cwd on a removed inode, and the next command fails with getcwd: cannot access parent directories. That's the situation column_is_terminal already forces a fresh pane for — it was my reset sequence, not a product bug. Noting it because it produced one convincingly wrong-looking run before I spotted it.

Checks

cargo clippy -D warnings · cargo test --lib 568 (+2) · tsc · eslint · vitest 444.