The agent loop previously kept running when the LLM emitted final_answer with
malformed JSON arguments: observe.analyzeResponse strictly json.Unmarshal'd the
raw args and returned isDone=false on failure, while act.runToolCall separately
repaired the JSON and executed the tool. The mismatch made final_answer
non-terminal, so the LLM saw its own answer in the next round's tool result
and re-emitted final_answer, surfacing near-identical answers multiple times
to the user (issue #1008).
Fix by unifying parsing in a new tools.ParseFinalAnswerArgs helper with three
fallbacks (strict -> RepairJSON -> regex extraction) and making final_answer
always terminal in analyzeResponse. When no answer can be recovered, emit a
user-visible fallback message and a Done=true event so the UI still resolves.
Also route final_answer.Execute through the same helper so tool execution and
loop termination stay consistent.
Adds regression tests in observe_test.go and final_answer_test.go covering
valid args, RepairJSON recovery, unrecoverable args, and garbage input.
Refs: Tencent/WeKnora#1008
wizardchen