What you learn, in order.

429s bounce off the wall and the agent backs off: 0.5s, then 1s, then 2s. A 400 shatters, and it is not retried.

messages and roles · sampling · stop reasons · tokens and pricing · streaming · retries and backoff · structured output

• a client that retries 429s but not 400s
• a parser for JSON a model wrapped in prose

Every turn pours more history into the window. Left alone it spills over the rim; compacted, the oldest turns press into a summary.

system prompts · few-shot examples · context budgets · ordering and recency · compaction · prompt caching · extended thinking

• a context builder that fits a token budget
• a history compactor that keeps what later turns need

The query is a beam. Cosine similarity is the angle between it and each document: the ones it lights up most are the top five the model reads.

embeddings · chunking · BM25 · hybrid fusion · reranking · HNSW · recall@k and nDCG

• hybrid search with reciprocal rank fusion
• the Production RAG build, scored on SciFact

Each claim sends a thread to the passage words it shares. The claim whose thread finds nothing is flagged instead of shipped.

retrieve then generate · citations · groundedness checks · no-answer handling · multi-hop · retrieval as a tool

• a pipeline that returns citations
• a checker that flags unsupported claims

The schema is a lock. Arguments that fit open the tool; the rest jam, and the exact error goes back to the model.

JSON Schema tools · descriptions that steer · argument validation · parallel calls · errors as results · side effects · tool search

• a dispatcher that validates arguments
• a parallel executor with per-tool timeouts

The agent laps the loop: call the model, run the tool, read the result, decide. When the model says end_turn, it takes the exit to the answer.

stop_reason control · turn and budget limits · message state · cancellation · approval gates · checkpoint and resume

• the loop itself
• a loop that stops inside a dollar budget
• a loop that resumes after a crash

The orchestrator splits the work into three streams. They run at once, and the merge gate opens only when the slowest arrives.

prompt chaining · routing · parallel sections and voting · orchestrator and workers · evaluator and optimizer · plan then execute · reflection

• a router with a fallback
• an orchestrator that fans out and merges

Every message falls onto a sieve. Chatter falls through; lasting facts stay. When two share a key, the newer overprints the older, and recall finds it.

scratchpads · conversation memory · long-term stores · write policies · forgetting and conflicts · per-user isolation

• a memory store with a write policy
• recall that prefers the newer of two facts

Each subagent fills its own bubble of context, so nothing leaks between them. Only small summaries float up to the supervisor, and every bubble is billed.

subagents · handoffs · supervisors · shared state · context isolation · fan-out cost · failure propagation

• a supervisor that delegates to subagents
• a handoff that carries only what the next agent needs

One cable, one protocol. The client and server agree on capabilities, list the tools, then call one. Any server plugs in the same way.

hosts, clients, servers · tools, resources, prompts · stdio and HTTP transports · capability negotiation · auth

• an MCP server for a local dataset
• a client that discovers and calls its tools

The agent types a patch, runs the tests, reads what failed, and patches again, until every bulb is lit or the budget runs out.

repo navigation · applying patches · test-and-fix loops · sandboxed execution · browser actions · verifying outcomes

• a patch applier that survives drift
• a loop that runs tests until green or out of budget

Each row is one episode of five tries at 80% success. pass@5 needs one head; pass^5 needs all five. The live estimates converge on the formulas.

outcome and trajectory evals · test sets · deterministic replay · LLM as judge · pass@k and pass^k · regression suites · benchmarks

• a trajectory grader
• a judge calibrated against human labels

A lens runs along both recordings frame by frame. At the first frame that differs it stops: that is the bug. Everything after is static.

traces and spans · GenAI semantic conventions · first divergence · replay · loop detection · tool error rates

• a trace differ
• a detector for an agent stuck repeating itself

Four tool calls, the same tokens either way. One after another, every hourglass waits for the last; in parallel, you wait only for the slowest.

token budgets · prompt caching · model routing · batching · parallel tool calls · context pruning · early exit

• the same agent at half the tokens
• a cascade that tries the small model first

Private data, an injected instruction, and a pipe to the outside. With all three open, data leaks. Close any one valve and nothing leaves.

prompt injection · the lethal trifecta · least-privilege tools · sandboxing · secrets · approval for irreversible actions · exfiltration

• a tool gate that blocks exfiltration paths
• a fix for an agent that obeys a poisoned web page

Both climbers fall at ledge 4. Without checkpoints one starts again from the ground and repeats three ledges; the other respawns at its last flag.

durable execution · queues and background runs · streaming UIs · prompt and model versioning · monitoring · fallbacks · feedback loops

• a run that resumes where it failed
• a rollout that compares two prompt versions