[r/boards] thread freezing

[salmad3]

Context:

Thread freezing is necessary to prevent any further modifications to a specific thread upon meeting freezing criteria or as determined by CommonDAO. This includes editing its content, adding replies, flagging, or deleting it. Once frozen, the thread should be immutable regardless of any existing permissions. Only users with the freeze privilege may reverse this state by unfreezing the thread.

Follows: #3755
Related to: #3820

Acceptance Criteria:

• Extends the Thread struct (or the Post struct when representing top-level posts) to include a Frozen boolean field.

  Example

  type Thread struct {
      ThreadID   string
      Title      string
      Author     Address
      Content    string
      Timestamp  time.Time
      Flags      []Flag
      Frozen     bool // indicates whether the thread is frozen
      // ... other fields
  }

• Implements a FreezeThread(boardID BoardID, threadID PostID) function that:

  • Verifies that the thread is not already frozen.
  • Checks that the caller has the required freeze permission (e.g., PermissionThreadFreeze).
  • Sets the thread's Frozen flag to true, effectively blocking all modifications.
  Example

  func FreezeThread(boardID BoardID, threadID PostID) {
      board := mustGetBoard(boardID)
      thread := mustGetThread(board, threadID)
      if thread.Frozen {
          panic("thread is already frozen")
      }
  
      caller := std.GetOrigCaller()
      args := Args{boardID, threadID}
      board.perms.WithPermission(caller, PermissionThreadFreeze, args, func(Args) {
          // Double-check to handle race conditions
          thread := mustGetThread(board, threadID)
          if thread.Frozen {
              panic("thread is already frozen")
          }
          thread.Frozen = true
      })
  }

• Creates an UnfreezeThread(boardID BoardID, threadID PostID) function that:

  • Validates that the thread is currently frozen.
  • Verifies that the caller holds the freeze/unfreeze permission.
  • Sets the Frozen flag to false.

• Overrides Existing Permissions

  • Once a thread is frozen, all modifying actions (editing, replying, flagging, deleting, etc.) are blocked—even if the caller would normally be allowed to perform these actions.
  • Relevant functions (e.g., EditThread, DeleteThread, FlagThread) include a check for thread.Frozen and reject modifications if set.

• Tests

  • Verifies that freezing a thread prevents any modifications.
  • Confirms that only authorized users (those with freeze permissions) can freeze or unfreeze a thread.
    -Attempting to freeze an already frozen thread results in an error.
  • Validates that once unfrozen, the thread can again be modified as normal.

[x1unix]

Implementing this alongside #3820

[x1unix]

#3829