Patrones conversacionales y herramientas agentic

Scenario 7 of the exam is Conversational AI Architecture Patterns. The first thing it tests is whether you understand that the Claude API is stateless: the model keeps no memory between requests.

Every turn you send the full message history in the messages array. "Memory" in a conversational app is something you engineer client-side, not a server session the model holds for you.

• system carries persistent instructions
• messages carries the entire turn-by-turn history, every request

In multi-turn chat, instructions that must hold for the entire session belong in the system field, not buried in a user turn 20 messages ago.

Why this matters: models exhibit lost-in-the-middle behavior, attending more to the start and end of the context than the middle. An instruction wedged in turn 7 of a 40-turn chat is the easiest thing for the model to drift away from.

The system prompt is re-supplied verbatim on every request, so it is the most reliable home for persistent rules: tone, role, refusal policy, output constraints.

Conversational turns end on a stop_reason. You drive your control flow off this signal, never by scanning the assistant's text for words like "done" or "finished."

• end_turn — the model completed its reply
• tool_use — the model wants a tool run before continuing
• max_tokens — output was truncated
• stop_sequence — a configured stop sequence fired

Parsing text for completion signals is a classic exam anti-pattern and almost always a wrong answer.

Agentic tools turn a chat into an actor. The loop is fixed and simple:

• send the request
• inspect stop_reason
• if tool_use: run the tool(s), append the results to history, send again
• repeat until end_turn

Decisions are model-driven. An iteration cap is a safety net to prevent runaway loops — never your primary stop mechanism. You terminate on the stop reason; the cap only catches pathological cases.

When you run a tool, its result is appended back to messages as a tool_result block carrying the matching tool_use_id. The model reads that result on the next request and continues reasoning.

Reliability tip from the exam: trim verbose tool output to the relevant fields before appending. Dumping a 5,000-token raw API payload into history wastes the window, worsens lost-in-the-middle, and dilutes attention. Keep the fields the model actually needs to act.

For safe agentic tools, the description is the primary selection mechanism — not the tool name. The model routes by reading descriptions, so write them like a contract:

• purpose — what it does and when to use it
• return values — what comes back
• input formats with examples
• edge cases and applicability boundaries

Overlapping or ambiguous descriptions cause misrouting. Aim for 4-5 tools per agent; past ~18 tools, selection reliability degrades sharply. Scope tools tightly to the role.

tool_choice controls whether and how the model uses tools on a given turn:

• "auto" — the model decides between answering in text or calling a tool (the conversational default)
• "any" — the model must call some tool; this guarantees structured output
• {"type":"tool","name":"X"} — force a specific tool

In open conversation you usually want "auto" so Claude can chat or act as appropriate. Reach for "any" or a forced tool when you need a structured, schema-validated result rather than free text.

Real conversations are messy. When the user's request is ambiguous, the safe pattern is to ask for more identifiers — never guess.

Classic exam case: a lookup returns multiple customer matches. The correct behavior is to request a disambiguating identifier (email, order id), not to silently pick the first row. Guessing risks acting on the wrong account.

For emotional or frustrated users the pattern is: acknowledge the emotion, propose a concrete solution, and escalate only if the request is reiterated.

"Safe tools" means a sensitive action cannot fire without its guarantees met. Two layers do this:

• Programmatic preconditions — e.g. block process_refund until get_customer returns a verified id. This is a deterministic guarantee prompt guidance cannot give.
• Hooks — PostToolUse intercepts results before the model sees them; outgoing-call hooks block policy-violating actions (e.g. refund > $500).

Hooks are 100% deterministic; prompts are ~90% probabilistic. Enforce critical rules with hooks/preconditions whenever failure has financial, legal, or safety consequences. Enforcing such rules with prompts alone is an anti-pattern.

An agent recovers only as well as its errors let it. A generic "Operation failed" blocks recovery; a structured error enables intelligent routing.

Distinguish an access failure (maybe retry) from a valid empty result (no matches — do not retry). Structured fields to surface:

• errorCategory — transient / validation / business / permission
• isRetryable
• attempted_query and any partial_results

Recover transient faults locally in the subagent; escalate non-recoverable failures with partial results. Never silently suppress an error, and never abort the whole conversation over one failed tool call.

As a chat grows, you must manage the context window without losing facts. Progressive summarization compresses old turns — but it makes numbers, percentages, and dates vague.

The fix: pull transactional facts (order ids, amounts, dates, verified identity) into a separate "case facts" block kept verbatim, outside the summary. Summarize the chatter; never summarize the facts the agent must act on.

Combined with trimming verbose tool output and placing persistent rules in system, this keeps multi-turn agents accurate across long sessions.

A scenario-based decision from Scenario 8 (Agentic AI Tools).

Lock these in for the exam:

• Stateless model — you resend full messages history every turn; "memory" is engineered client-side.
• Persistent instructions live in system; mid-history rules get lost in the middle.
• Stop reasons drive control flow — loop on tool_use, finish on end_turn; never parse text for "done".
• Caps are safety nets, not the primary stop.
• Tool descriptions (not names) select tools; 4-5 per agent, scoped to role.
• tool_choice: auto to chat-or-act, any to guarantee structured output, forced for a specific tool.
• Ambiguity → ask for more identifiers, never guess.
• Safe tools = preconditions + hooks (deterministic) for financial/legal/safety rules — not prompts alone.
• Structured errors enable recovery; keep case facts verbatim outside summaries.