[Critical] 41 endpoints return "api-error-generic" literal instead of the real error — Fluent key never defined

Severity: Critical
Domain: Error handling

Location

41 call sites (rg -c 'api-error-generic' → agents.rs:31, tools_sessions.rs:10), including:

• crates/librefang-api/src/routes/agents.rs:3066, 3105, 3156, 3209, 3319, 3399, 3465, 3585, 3631, 3675, 3764, 3843, 4032, 4336, 4479, 4839, 5266
• crates/librefang-api/src/routes/tools_sessions.rs (10 sites)

Every site has the shape:

t.t_args("api-error-generic", &[("error", &e.to_string())])

Problem

The Fluent key api-error-generic is never defined. grep -rn 'api-error-generic\s*=' against crates/librefang-types/locales/{en,ja,zh-CN,de,fr,es}/errors.ftl returns 0 hits. The fallback at crates/librefang-types/src/i18n.rs:163-164 returns key.to_string() on missing key, so the {$error} interpolation never runs.

Result: every one of those 41 HTTP 500 responses returns {"error": "api-error-generic"} to the client. The actual e.to_string() is silently dropped — not interpolated, not logged at most sites. Operators have no diagnostic information on a class of 5xxs that includes the bugs reported in "agent-not-found-returns-500", "rusqlite-errors-leak", and the agent_clone 500-on-AgentAlreadyExists case folded into the same item.

Fix

Stopgap (one line per locale): add to every errors.ftl:

api-error-generic = { $error }

Long-term: route all 500s through a typed helper that logs the full error chain server-side and emits a stable scrubbed message client-side. The MemoryRouteError pattern at crates/librefang-api/src/routes/memory.rs:198-215 is the correct shape.

Tests

• Reflection test: every t_args key used in route handlers exists in every errors.ftl.
• Integration: force an internal error (e.g. corrupt session DB) and assert the response body contains the actual error context, not the literal "api-error-generic".