
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
In triangle $\triangle ABC$, $a$, $b$, and $c$ are the sides opposite to angles $A$, $B$, and $C$ respectively. The vectors $\overrightarrow{m} = (b, 2a-c)$ and $\overrightarrow{n} = (\cos B, \cos C)$, and $\overrightarrow{m} \parallel \overrightarrow{n}$.

(1) Find the magnitude of angle $B$;  
(2) Let $f(x) = \cos(\omega x - \frac{B}{2}) + \sin \omega x$ ($\omega < 0$), and the smallest positive period of $f(x)$ is $\pi$, find the intervals of monotonicity for $f(x)$.

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