cookbook(llamaindex): pass memory= to agent.run(), not ReActAgent constructor

[DK09876]

Summary

Brings the memory= fix from cookbook/llamaindex-react-agent (commit 668fc27) into main as a fresh PR. The fix existed but was never merged back after PR #18 landed.

Why this is needed

Pattern 1 (HindsightMemory as a drop-in BaseMemory) silently broke in the cookbook under LlamaIndex 0.14.x:

• Under LlamaIndex ≤ 0.12, llama_index.core.agent.ReActAgent was the legacy class whose constructor accepted memory=BaseMemory. The original cookbook used ReActAgent(tools=[], llm=..., memory=memory, ...).
• LlamaIndex 0.14 routed llama_index.core.agent.ReActAgent to the workflow-based class. Its constructor has no memory field; the kwarg is silently swallowed by trailing **kwargs: Any and ignored.

End-user symptom: cell 7 (the cross-session recall demo) returned "I don't have access to that information" (or the same in Spanish) even though cell 5 supposedly stored Alice's facts. The HindsightMemory hooks never fired because memory wasn't actually attached to the agent — aput/aget were never called.

Workflow agents accept memory= as a kwarg to run() instead. This PR splits create_memory_agent to return (agent, memory) and threads memory=memory through agent.run(...) in cells 5 and 7.

Changes

• Cell 3: create_memory_agent returns (ReActAgent, HindsightMemory) instead of just ReActAgent. Drops memory= from the ReActAgent(...) ctor call.
• Cell 5: agent, memory = create_memory_agent("alice") then agent.run("...", memory=memory, max_iterations=10).
• Cell 7: same change for the cross-session recall.

Total: 1 file, 9 insertions, 7 deletions.

Relationship to other PRs

• Pairs with the integration fix in fix(llamaindex): default to Cloud + replace dead manual test with gated E2E + requires_real_llm bucketing hindsight#1867 commit 47bcac45 (HindsightMemory.aget falls back to last user message when input=None). Both layers need to be in place for end-user UX to work end-to-end.
• Supersedes the unmerged tail of cookbook/llamaindex-react-agent (7 commits ahead of main, including 668fc27 fix: pass memory to agent.run() instead of constructor).
• Closed PR cookbook: sharpen Pattern-1 prompts in 08-llamaindex + 10-openai-agents #38 (Pattern-1 prompt-polish) and merged PR cookbook: add LlamaIndex ReAct agent notebook #18 are not affected.

Test plan

• Cookbook 14/14 cells execute against canonical PR #1867 build of hindsight_llamaindex, 0 errors.
• Cell 7 (Pattern 1 cross-session) now returns the recalled facts (verbatim "VS Code as your IDE" surfaced) instead of "I don't have access".
• Pattern 2 (HindsightToolSpec, cell 23) and Pattern 3 (factory tools, cell 26) still pass.
• Reviewer to verify against published hindsight-llamaindex once #1867 is merged.

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