
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 triangle with internal angles $A$, $B$, $C$ and the lengths of the sides opposite these angles are $a$, $b$, $c$ respectively. Let vector $\overrightarrow{m}=(2a-c,b)$ and $\overrightarrow{n}=(\cos C,\cos B)$. If $\overrightarrow{m} \parallel \overrightarrow{n}$,  
$(1)$ Find the magnitude of angle $B$;  
$(2)$ If the area of $\triangle ABC$ is $\sqrt{3}$, find the minimum value of side $AC$ and describe the shape of the triangle at this condition.

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