Assignment fan-out: wrap the loop body in try_catch so one failing person does not abort the fan-out

[os-warren]

Closes #123

What was wrong

loop-node.ts iterates its body with a bare await engine.runRegion(...) and has no try/catch of its own, so a body node that fails throws straight out of the container. The first bad assignee ended the whole run, every later assignee was never processed, and — because an aborted loop never returns its childSteps — the rows it had already written were not counted either.

Measured on the real engine at origin/main, three names with the middle row bad (a blank assignees entry — the "missing owner" shape):

	before	after
run	status: failed	success
run summary	acted: 0	acted: 2
duly_task rows written	1	2
duly_assignment.task_count	1	2
what the assigner is told	nothing	one inbox warning naming the row and the reason

What this does

The loop body is now one try_catch container. The three data nodes that do one person's work sit in its try; the catch runs notify to the assigner, once per assignee who got no task.

What the assignment shows afterwards — decided here so it is a contract, and written into the flow's header comment:

1. The count is the truth. task_count is a Field.summary over the children, so it reports the tasks that actually exist. The run summary now agrees with it, because a loop that completes returns the childSteps an aborted one threw away.
2. The failure is named to the assigner, in their inbox: the assignee handle, the engine's own reason, severity: warning, and a click-through to the assignment. The run log alone does not count — it is an operator surface and the assigner never opens it.

Two decisions worth reading as decisions rather than as details:

• The flow still writes nothing back onto duly_assignment — not a note, not a status. It cannot: the start trigger is record-after-write, so a write to the trigger record re-enters this same flow on a row still dispatched, and the notification would be re-sent on every re-entry. The inbox is the assigner-visible surface that costs no such loop. (The existing invariant test "the flow never writes duly_assignment" still holds.)
• The handler reads {fanout_assignee} and nothing else about the person. The iterator is re-bound before every iteration; fanout_assignee_user is not. A region that throws at fanout_find_unit leaves that variable holding the previous iteration's row, so a handler that read a name from it would calmly name the wrong colleague. test/assignment-fanout.test.ts pins this both structurally and against the engine.

Two changes that came with it

Both are required by the above rather than incidental, so they are called out rather than buried:

• src/email-templates/assignment.email-template.ts (new, en + zh-CN). NotifyConfigSchema makes inline title/message and template mutually exclusive and its own .describe() calls the inline path "not localizable", so AGENTS.md §8 is only satisfiable on the template path. assignee is deliberately not a required render variable: the commonest bad row is an assignee entry that is itself blank, and a required-but-absent hole would dead-letter the one message whose job is to report it.
• src/translations/authored-text.ts — two REENTER entries (config.try, config.catch) so the i18n walk knows a try_catch's regions re-enter the flow vocabulary, exactly as loop.config.body already does. Without them every node inside the new regions is an unclassified path and test/i18n-coverage.test.ts fails naming all 30 of them. parallel's config.branches[] is deliberately not added: a branch carries a name that would land on the flow.name verdict and be misread. ⚠️ This file sits in src/translations/, which Retire the three i18n exemptions once the platform ships their keys — and re-take the two English-island screenshots #106 is also working in — the two lines are in the REENTER table, away from the locale bundles, but the PM should sequence the merges knowingly.

test/email-templates.test.ts's notify walk now recurses into container regions. Without that it silently stopped covering the newest notify node, whose template miss would dead-letter permanently while the run still reported success.

Verification, at 9715f88

All four gates green on this exact commit:

pnpm validate   → Validation passed (41 author-time rules); only the expected
                  hierarchy-security warning AGENTS.md says must stay
pnpm typecheck  → exit 0
pnpm test       → Test Files 35 passed (35) · Tests 884 passed (884)
pnpm build      → Build complete

The 17.3.0 lint the card was raised by — checked read-only in this worktree, and checked in both directions so "no warning" is a measurement rather than an absence:

• npx @objectstack/cli@17.3.0 validate on this branch: exit 0, 42 author-time rules, no try_catch warning.
• Same command with origin/main's pre-fix flow restored in place: the warning fires three times, verbatim as quoted in the issue (fanout_find_existing / fanout_find_unit / fanout_create_task). Restored afterwards; the tree is byte-identical to the commit.

Reverse verification of the new tests. With the catch region ablated from the committed flow (tests untouched), test/assignment-fanout.test.ts goes 9 red / 30 green — every engine assertion plus the two handler-structure ones — with expected [ alice ] to deeply equal [ alice, carol ] and try_catch 'fanout_attempt': try region failed — … Owner is required. The ablation script restored under a trap … EXIT INT TERM; the mutation was confirmed on disk by grepping the marker to 0 before the run and back to 1 after.

One thing this could not test the obvious way. This repo installs no record_change trigger — they ship as separate @objectstack/trigger-* packages and only trigger-schedule is a devDependency — so a duly_assignment insert fires nothing and the boot says so. The engine test drives the flow with automation.execute(flowName, context), which is the same door the trigger uses: registerFlow arms every trigger with trigger.start(binding, (ctx) => this.execute(flowName, ctx)). Which context a record-change fire would assemble is pinned separately by the start-node assertions already in the file. This is written into the test's own header.

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