
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given a sequence $\{a_n\}$ where each term is positive and satisfies $a_{n+1}^2 = 2a_n^2 + a_na_{n+1}$, and $a_2 + a_4 = 2a_3 + 4$, where $n \in \mathbb{N}^*$.  
(1) Find the general formula for the sequence $\{a_n\}$.  
(2) Find the sum of the first $n$ terms of the sequence $\{na_n\}$.

Present the answer in LaTex format: \boxed{Your answer}
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