APL (Dyalog Unicode), 34 bytes^SBCS

Anonymous prefix lambda.

{∊((⊃⍴⍨2|≢),+⍨⍴⍨∘⌊2÷⍨≢)¨⍵⊂⍨2≠/0,⍵}

[Try it online!][TIO-jq3pxrjk]

{…} dfn; ⍵ is right argument

0,⍵ prepend a zero to the argument

2≠/ pairwise inequality mask

⍵⊂⍨ use that to partition (true means begin new partition here) the argument

(…)¨ apply the following tacit function to each run of equal numbers:

≢ the length of the run

2÷⍨ let 2 divide that

⌊ floor that

∘ then

⍴⍨ use it to reshape…

+⍨ the doubled (lit. addition selfie) run

(…), append that to the following:

≢ the length of the run

2| division remainder when divided by two (1 for odd length runs, 0 for even length runs)

⊃⍴⍨ use that to reshape the first element of the run

∊ enlist (flatten)

[TIO-jq3pxrjk]: https://tio.run/##SyzI0U2pTMzJT///v/pRR5eGRp1RzaPORZqP2iY/6mrW0X7Uu@JR7xYQ2THjUU@X0eHtIDZQwSGg@NZHXU1ArtGjzgX6BjpAfu3/tEdtEx719j3qm@rpDzTg0HrjR20TgbzgIGcgGeLhGfw/TeFR7xquNAUjHRAyASI4B8rXUbBAFjICciDCQI4FGIGEDA2MgEIQ0tTQCEoYmZqBCaACYx0oMgQjc6AKOAIA"APL (Dyalog Unicode) – Try It Online"

APL (Dyalog Unicode), 34 bytes^SBCS

Anonymous prefix lambda.

{∊((⊃⍴⍨2|≢),+⍨⍴⍨∘⌊2÷⍨≢)¨⍵⊂⍨2≠/0,⍵}

Try it online!

{…} dfn; ⍵ is right argument

0,⍵ prepend a zero to the argument

2≠/ pairwise inequality mask

⍵⊂⍨ use that to partition (true means begin new partition here) the argument

(…)¨ apply the following tacit function to each run of equal numbers:

≢ the length of the run

2÷⍨ let 2 divide that

⌊ floor that

∘ then

⍴⍨ use it to reshape…

+⍨ the doubled (lit. addition selfie) run

(…), append that to the following:

≢ the length of the run

2| division remainder when divided by two (1 for odd length runs, 0 for even length runs)

⊃⍴⍨ use that to reshape the first element of the run

∊ enlist (flatten)