What are four events that foreshadow Sydney Carton's saving the life of Charles Darnay in A Tale of Two Cities by Charles Dickens?

In his novel that is replete with doubles, Charles Dickens frequently foreshadows the switch of Sydney Carton for Charles Darnay at the end of the narrative. This foreshadowing occurs in the development of different instances throughout the narrative.

Here are four such instances:

1. In Chapter 3 of Book the Second, Charles Darnay stands before the London court charged with treason for having spoken against King George on the Dover coach. A witness named John Barsad cannot positively identify Darnay because he is unable to distinguish Darnay from the barrister, Sydney Carton, who is sitting at the prosecutor's table. After having asked Barsad to look at both Carton and Darnay, the Attorney-General Stryver asks him,"How say you? Are they very much alike?" When the witness has to admit that they are, indeed, too much alike for him to make a positive identification of one, Stryver is then able to discredit all to which the witness has attested.
The fact that these two men are indistinguishable foreshadows the credibility of their eventual switch so that Carton can save Darnay's life by taking his place at the guillotine.

2. After the trial in Chapter 4 of Book the Second, Carton invites Darnay to share a meal. At a tavern they talk, but Darnay feels as though he is in a dream with his "Double of coarse deportment." Oddly, Carton asks Darnay,

"That's a fair young lady to be pitied and wept for by! How does it feel? Is it worth being tried for one's life, to be the object of such sympathy and compassion, Mr. Darnay?"

This question, of course, is prophetic since this is precisely what will happen to Carton. When he goes to the guillotine for Darnay, Lucie will make him the object of such compassion. 

3. In Chapter 13 of Book the Second, Carton visits Lucie and tells her he will do anything for her and her family: "For you and for any dear to you, I would do anything." Later, he tells her that she has stirred in him the ashes of his old desires to achieve something: "...you have been the last dream of my soul...."
Before he leaves, Sydney tells Lucie to remember him as "a man who would give his life to keep a life you love beside you."

These lines allude to the previous conversation of Carton with Darnay at the tavern and further foreshadow the sacrifice that Carton will make for Darnay, as well as revealing the depth of Carton's feelings.

4. In Chapter 12 of Book the Third, when Sydney Carton enters the wine shop, Madame Defarge mistakes him for Charles Evremonde (Darnay). This act of mistaken identity by the sworn enemy of the Evremondes underscores how closely the two men resemble one another and how it is possible for Carton to replace Darnay in the prison. In fact, in this scene, Carton may well be testing how much he does resemble Charles Darnay. For, if Mme. Defarge looks at him intently, then he can know that his similarity to Darnay is, indeed, very close. This scene also foreshadows Carton's death as Mme. Defarge speaks with vehemence against Charles when her husband asks her if her retribution is not too extreme.