Actually, he didn't sign the articles until June 2nd. The 26th was the date of the Union officers' interview and negotiation with Kirby Smith's and Canby's representatives. In Kirby Smith's case, his representative was Gen. Simon Buckner.
I'm looking for my source (it isn't Fehrenbach), but the main Confederate encampment in Texas, east of Houston, didn't break up until a day or two after Gordon Granger showed up in Galveston on June 19th and started running his mouth nonstop about illegality, null and void, and blah, blah, blah.
The Confederate troops didn't just disappear because Edmund Kirby Smith inked a document and pointed his horse toward Mexico. What did disappear was much of the Confederate chain of command and Confederalized Texas troops' legal basis for resistance to the 25,000 men Phil Sheridan was leading by sea from City Point, Virginia en route Texas to reinforce Granger in Galveston and the small garrison (reduced by the battle at Palmito Ranch on May 13 -- correction to date) at the mouth of the Rio Grande.
The State of Texas never signed a surrender document, and so perforce neither did its People in arms as the Militia. Of course, if Texas did surrender, you're free to produce the surrender document, it'll be a useful addition to the discussion. I would encourage you to spend as much time as possible looking for it.
But Kirby Smith's instructions came from the Confederate governors of Arkansas, Louisiana, and Mississippi, not from Texas.
One last note: the last reference to fighting (on land, anyway) that I can find is to a skirmish that took place near Rocheport, Missouri, on May 24, 1865, between federal troops and Confederate irregulars.
Actually I've seen May 30th quoted as the date of surrender as well. But regardless of whether it was May 26th or May 30th or June 2nd surrender he did. And in doing so he surrendered all the troops in Texas since those came under his command.
The State of Texas never signed a surrender document, and so perforce neither did its People in arms as the Militia. Of course, if Texas did surrender, you're free to produce the surrender document, it'll be a useful addition to the discussion. I would encourage you to spend as much time as possible looking for it.
I realize that abiding by the constitution was not a southern strong point, but considering that the confederate constitution says that states may not engage in war without consent of congress or enter into compacts or agreements with a foreign power, then it would be ridiculous to believe that Texas could legally sign any peace treaty.
I don't have it at hand, although it is uploaded to the net, but i am sure i have seen in the operational narrative section of some Ohio and Kentucky (US) regiments in Dyer citations for operations against guerrillas in Kentucky as late as June 1865.